I looked up Trimovate, it's a steroid with added antibiotic and antifungal agents. If your problem isn't fungal or bacterial, it may not have any effect - but do talk to a pharmacist about it.
Are you using footcare products? Could you be allergic to any of the ingredients?
What medication are you on? The patient information leaflets will give details of side-effects, so do have a look to see if that could be the problem.
Eating a lower carbohydrate diet can take a bit (a lot) more effort than just grabbing sandwiches/cereals/chips, but can significantly improve control of blood glucose levels. Lots of help available here - just post your questions!
Is weight a factor for you? Since losing shedloads (technical term), my feet no longer swell up in hot weather.
Good luck getting to the bottom of the problem - and it's definitely worth making an appointment to see the doctor. All we can do here is describe what's worked for us - we're not medically trained.