Thanks for posting your query.
Yes, it could be because of HIV, but HIV is not the only cause for it. It may be just the routinely seen aphthous ulcers
, other viral fever
eruptions, due to acute streptococcal sore throat
The reasons are many.
It is good that you have taken the Co-amoxiclav
You will be fine soon.
If in doubt, you can get yourself tested for HIV by the HIV combo tests that are available.
Hope this helps.