Can someone get HIV from oral sex four months ago?

Hello doctor,

I wanted to know if I need to get tested for HIV. About four months ago, I had what I thought was oral sex with a girl. I did not give her cunnilingus for long, but I cannot remember entirely. About a week after this happened, I got tested for STDs like chlamydia, gonorrhea, and some other stuff that came back undetected. I cannot remember how long it was. Still, I started having what I think are HIV symptoms like fatigue, unexplained diarrhea, and an unexplained rash on both of my arms. Still, my arms were burning a little when I would touch them, and it only came up to my shirt line, so I assumed it was a heat rash from sunburn because I was on track practice that day. I do not know what to expect or do because I am afraid if I do not get tested, I will have AIDS later. I have learned that the oral sex risk of HIV is small, but I want to be sure.