It's not impossible that you have had some sort of reaction to physio you had this week, you said you had seen the physio earlier this week. Despite you trying to explain so many details it's difficult to say exactly online what is wrong as we can't assess you. Sounds like something has provoked an acute flair up of a chronic problem.
Did the physio warn you at all about any possible exacerbation of symptoms after the last treatment?? Did he say what could be expected? Does he have a locum or is he somewhere possible to contact on his mobile phone?
Warm pack may make symptoms worse if it's acute new pain. Trying cool or colder might well work. Or various hot /or cold stuff to apply like sport cremes etc. Anything working on your pain nerve endings in the skin can potentially stop pain for a while and give some relief, if only temporarily. (I'm not sure how big an area you are hurting in)
If it doesn't start to get better ie less pain very soon and your pain killers aren't helping at all, a different medication from your GP may help. Pain comes in various forms and the mechanisms for combating it are not always the same. If the symptoms are really so different to normal and it's worrying, do go to your doctor (preferably the one who knows your case history best)and ask or at least phone up. It may well be that he doesn't know any more than a physio who has been treating you for a while, but he could reassure you that it's nothing awfull if he sees you. I hope this is the case.