Anti Histamines make me tired

A lot of antihistamines will cause drowsiness - even the ones that say they don't - on the info sheet you will find the warning that they may!
What investigations have you had? I suggest going back to try to find the root cause.
Also, you don't say how obese you are - and whilst it doesn't help any health issues, you shouldn't blame it for everything!
Have you had any investigations into tiredness? It can be a symptom of a ot of things.
I suggest an appointment with your GP (or practice nurse / nurse practitioner - who can be very helpful) and if they blame obesity, say something like "I am tackling this, but it feels like a circular problem, and I'd like to see if anything else might be causing the tiredness".
Also, although this might not be the cause, some people find some fruits (especially raw apples & peaches) cause the kind of itching you describe. Whilst sorting out an appointment, you could just try cutting them out to see if it helps.
Good luck.