Looking for some advice

It does sound like a job, you certainly do a lot and if you can’t get out it’s long days having to stay at someone else’s home. In my experience I would have preferred my GC to be brought to my home when they can get used to my house plus it’s easier to occupy yourself in your own home when they are asleep, occupied etc.
Anything more than one day a week is a chore ie a job, and even one regular day a week can also get to be a tie because often your things have to be moved around or missed if it’s one particular day.
I do understand, and have had that conversation, which was a bit awkward, but even one day a week was a restriction. The other grandparent now sees the children and her adult child more than I see mine but it’s a price I am prepared to pay.
Given your health issues think it’s not unreasonable to want and need time fir yourself. As one gets older it gets harder and you have other children and grandchildren you presumably would like to see too.
Finally if your gc is 3 it’s possible that a second child may follow soon and if you are still enmeshed in this high level of child care they will probably expect you to continue.
You are not being unreasonable in wanting time fir yourself.

You are doing a huge amount if childcare! One day a week is enough for me . I love my Grandma duty and have a good relationship with my AC.
Your health is your priority. Child not allowed in your car ? You also say that when you are in their house you cannot leave, is that because there is no where to go or because your son and his partner do not want you to take your GC out? You have other GC and the other Gran does not , this makes a difference. So much childcare is very restrictive and impinges on your personal life. IMO that is unreasonable. Obviously I am unaware of the background story , however that does not change the fact that you are now weary of your responsibilities. Time to speak out and explain your feelings, so many parents expect so much from Grandparents. This may cause trouble but you must put your health first .

singlegram you have to be upfront with them. I had a similar issue with my youngest son. I was asked to do pick-ups about 3 days a week. I had to decline, because I was already committed to my daughter’s children and could not chop and change with daughters in-laws.
I offered to babysit, if they wanted to go out in the evening for meals etc but just could not commit, as it would mean I had no free time for myself, and like you, I am on my own. They probably were miffed at first, but all is well now. And frankly,I had no qualms because they are highly paid professionals and could afford paid childcare.
I have a great relationship with the little ones and see them regularly.
Hope you manage to sort things out - from your post, I think you are in the USA, are you? Nice to have posters from the other side of the pond …

I really don't understand why you say you can't get out of child care duties SingleGram surely you just need to say that ill health prevents you continuing as before. Can you offer a reduced amount of time or help to pay for child care.
I think as Charleygirl5 says you need to to be clear about what you intend to do and give them a six week period to make alternative arrangements. I'm sorry if you feel that you then won't have much contact with your granddaughter but your health care is very important.

It's very difficult to know what to suggest when we don't know all the people involved, but are you able to sit with your son, tell him what you've told us and see what he suggests?

Do they pay you for this childcare? If not why not? That is a lot of childcare you are doing. And, why is she not not allowed in your car? Either they trust you to care for her or not. Bet, that rule will change very quickly as she gets older and they will want you to transport her to and from nurseries, schools, activities, etc.

You are being taken advantage of. It is up to you just to say quite clearly that you are unable to continue due to your own health issues, etc. Give them a good notice period, so they can make other arrangements. See if they would be willing to drop it down to once a week or a fortnight.

Also, point out that you really hope that they will understand that you still wish to continue a good relationship with this g.child and hope some sort of alternative arrangements can be put in place for you to see her reasonably regularly.

You need to enjoy your own life now. And they should be happy to understand that it is THEIR child (not yours) and THEIR responsibiltiy

Keep us informed as to how things go.

You are obviously not appreciated for the hard work that you are doing. It is a commitment and you want to be free. You have tried talking to her and that has not worked so sort out a last working day date and put it in writing.

It is up to you how much notice you give but 6 weeks I think is reasonable.

Decide if the reasons are your poor health or whatever but that will be asked I am sure.

Good luck.