Not wanting to go to work

Why are you considered to be vulnerable? If you are on the vulnerable list , then you can stay at home with no problems.
If your partner is vulnerable then maybe your manager will be sympathetic. However I don’t think that not wanting to go in is going to cut it with your boss, although he might let you have time off with no pay, but I doubt it
It sounds as though you have to make a choice about how much you want the job.

If you were fit enough to go back to work, why has that changed? You say you have been off for so long yet you went back for two weeks a month ago
Most, if not all supermarkets have effected hygiene measures to protect their staff so you should not be at any particular risk. .
The question is do you want this job?
If you walk away you will not be eligible for unemployment benefits will you?
You don’t say what qualifies you for the “vulnerable” category?
If you worked 2 weeks and then were told to self-isolate for 12 weeks on full pay perhaps that just appeals more than going to work?
Forgive me, but there are people out there on no pay because their job has disappeared and others in the front line who have not hesitated to put their job first.
By all means walk, but don’t be surprised if you find you have no job, no pay and other people are struggling to get their essential supplies.
Who was it said We’re all in this together?

Are you considered by the NHS as being vulnerable? By that I mean have you got heart or lung problems, or any life-limiting illness?

A lot of people are having to go to work and risk their health. I'm classed as a Key Worker because I'm the Warden of a sheltered housing scheme. I'm still working (mornings).

Your employer has a duty of care, so you should be given hand sanitiser and/or gloves, and customers shouldn't be too near to you. If you don't go, you may not have a job when all this is over.

I work in the university . I've been upgraded from old reliable dog's body to essential personnel and have to report for work on Monday . In another situation I might be flattered ?
I'm glad in a way to restart work ,as I can 't concentrate on anything apart from eating !

I am a key worker, I dont want to go to work, but it would not enter my head not to turn up.
I can understand your worry if you have underlying health conditions though.
Also do you need/want this job if you do you may have to think about going back.

Actually, I dont think you should have gone back if your sick note was still operative without permission from a medic. So I think you are lumbered!

Unless you are over 70 or have an underlying and continuing medical condition, you are not vulnerable.

You may have physical weaknesses and limitations on your stamina after your operation, but that does not mean that you are at a high risk of complications if you get Covid-19. A hip replacement is that and no more.

If when you get to work you have to stand more than you can cope with, then ask for a chair or transfer to a different role in the business, but a hip replacement does not put you in the vulnerable category.

It is daunting going back to work after a long lay-off, espcially under current conditions. Do not make a decision about twhat to do until you have made the effort aand been back at work for a few days. You may find that once you are in the shop and busy working all your worries and fears will disappear.