Welcome to HCM.
after a fat rich diet is not a usual symptom in HIV
. But at the same time many new type of presentations are coming day by day. HIV symptoms will not manifest immediately after suspected intercourse. It will take at least few years to manifest after the immunity gets very low.
Loose motion following fat rich diet indicates some digestive enzyme deficiency
. It may be an in-born error or may be due to some other recent pathology.
Anyhow test yourself for HIV if you have doubt.
Approach a physician and seek his help to diagnose your problem.
Get well soon