Thanks for providing more information.
Well i want to assure you that if your HIV test was negative so it is less likely to have AIDS and you shouldn't worry at all.
As you have recurrent outbreaks it is likely to be aphthous.
Stress can precipitate the condition.
Sometimes foods like eggs, cereals, almonds,chocolate, coffee, peanuts, cheese strawberries and tomatoes etc. can be the precipitating factor, though you did not notice any change.
Acid reflux can be another possible cause.
Sometimes the cause is unknown, sometimes it can occur due to an irritant in the mouth, it is also due to vitamin deficiencies as well.
It will be my recommendation to start having supplements of vitamin B1, B3, B12, C.
You can try chlorhexidine mouth rinse thrice a day.
Also before eating, half an hour prior, u can apply lignocaine mouth paint which will help you eat better.
Try metamucil if your have associated constipation,bloating,flatulence.
Also try OTC Prilosec to see if helps.
But if your symptoms'll persist then it needs to be seen by a doctor for precise diagnosis & sometimes steroid(triamcinolone acetonide orabase) may be necessary to cure it.
I hope this helps.
Please rate me highly (Star 5 Great Service), if you are satisfied with our conversation.
If you have any further query then feel free to ask.
Bonus and positive feedback are highly appreciated.