Christ on a bike cheeryface, are you me?
I have been through the whole have i got HIV thing, did i pass HIV to my child (in fact it had a massive negative impact on our relationship). I definately do NOT think you are barmy. You want barmy? Try going to the minor injuries clinic, hysterical because you think your tonsils are tumours! (AND i have a medically related degree!). That was me just before i was put onto citalopram (and with good reason wouldnt you say ). To put your mind at rest about the HIV - there is NO WAY you have HIV from this person, if you had contracted HIV 16 years ago, without treatment, you would be dead.
Here is the most likely explanation as to why you are constantly feeling ill - anxiety. It makes you ill. I have had all manner of symptoms - Headaches (that is pretty common for people under any type of stress), palpitations, tingling in my face and hands (self diagnosed MS of course - Doctor soon put me straight about that!), panic attacks, feeling sick, getting every cold and flu bug going because im so run down due to constant worry. You name it ive had it, or at least i have thought i have!
Someone pointed me to a website and i forget what it was about anxiety - and the physical symptoms it produces are staggering. Of course you then get anxious about the symptoms and so it goes on. That is the one thing i can say about citalopram, it stops things from playing on your mind and allows a bit of logic.
You say that you feel a balloon in your head, that could well be your sinuses - i am suffering (along with everyone i seem to know just now!) with my sinuses at the moment and it can feel like that. You don't feel any pain in your brain you know, there are no nerve endings. I bet you 50p though, its anxiety and once you can get that sorted, the headaches will go. Honestly, when i went to the docs with the tingling, she said, look, you haven't got MS (she did a load of tests right there and then that ruled it out - stuck me with pins so she did!) its anxiety and a very common symptom - miracle cure!!! It went away more or less within days. I get it if i am particularly stressed, but i mean through the roof stress.
So, the unprotected sex with the dodgy character is clearly something that bothers you - (been there done that) STOP using it to beat yourself up, its in the past and its done and not worth the thought processes. I can say this because i know that is exactly the sort of way i used to think, that i had HIV and quite frankly, i deserved it.
You need to see a counsellor, i think you will be banging your head against the wall until you do.
Hope this was not too blunt, but i can see so many parallels with myself (now i wish i could take my own advice).