"What else [other than HIV] could these ongoing symptoms be?" There must be 100 disorders that could do it; the symtoms do not sound at all like HIV infection, and your blood test shows that HIV cannot be the cause. One possibility is antibiotics. Loose and irregular stools are very common after a variety of antibiotics, including azithromycin.
For more information on HIV test timing, read the giant number of threads and my responses both on this forum and especially the STD Forum. Search the threads and archives for "time to positive HIV test". But the bottom line is that almost everybody who acquires HIV develops a positive antibody test within 6 weeks. Some sources continue to say 3 months to be absolutely sure, but it is really rare for a positive result to be delayed that long.
Bottom line: follow up with your own provider if your symptoms continue. But stop worrying about HIV; you don't have it. Best wishes--
HHH, MD
Sorry left this part out. To the best of my knowledge the only exposure to the Chlamydia or HIV would be from the 12/10 night. Unless boyfriend was with someone else. Don't think so but look what I did on 12/10 can't trust anyone not even myself! My gut tells me it came from the girl. At the time I didn't know how much she gets around but now I do.