early last month had two encounters with a sex worker. in the first time i had vaginal sex with a condom. but my penis was flaccid not fully hard..the condom did not slip of...i didn't notice at least..i finished really quickly wouldn't have been even a minute...i ejaculated outside into the condom condom was still on when i did. The second instance was a massage and a hand job that lasted an hr..should i be worried about this..i have been really worried and got tested 25 days and 28 days after .with Alere Determine HIV-1/2 Ag/Ab Combo..negative result...can this be considered a conclusive result or should i test later ? I do plan to test for other STDs in the coming weeks as well..since my 28th day test...I have been feeling a slight burning in my penis...it is not consistent as in present through out the day but..its there for a second or two and then it's fine again for sometime...almost feels like someone is pinching my penis for a few seconds minutes max and letting go..I have been worried sick...the past month has been really stressfull for me for a lot of reason and this is also driving me crazy..I am in a relationship which at the time of the incident was going through a tough time..since we have gotten back together and I did tell my girlfriend about this..is burning like this consistent with any std? Based on my experience what do I need to test for? Opinions on negetive hiv result at 28 days?