Ummm..first of all, wow. I mean you and her are going to hit all the markers needed to be considered a "high risk" to become infected and not just with HIV but also Hepititus which you need to be just as concerned about as the HIV if not more since it is spread even more easily than HIV.
Let's see, she is just a hot girl who has a lot of sex...key words here being she has s lot of sex
#2. Do you think just because someone is "hot" that they are less likely to be HIV+? If she was missing a couple teeth and pretty damn ugly would you be a little more worried?
#3. Everyone would say "oh no, I don't have anything" upon being asked. Do you really think she would tell you "Hmmm, there is a good possibility that I could have something" (which you should already know that that there is a good possibility she could have something because she sleeps around a lot and obviously she shares needles with people...surely you don't think you are the only one that she has shared a needle with)
#4. She obviously has NO problem sharing needles!
You definitely need to get some safer practices here or it is likely you will end up being exposed to something..and HIV/AIDS isn't the only thing you need to be concerned about...who do you think is one of the main groups of people who have Hepatitus? IV drug users who share needles and people having sex with many partners. And it is not even like you just made a mistake and shared needles only one but you did it again!
Also, "blister on your ass" is not on the list of symptoms of HIV/AIDS. You do realize how that whole thing works right? I think it is a necessity that you go get tested and see where you stand with your status as of now. But you have to be retested in 2 to 3 months (not sure of the exact waiting period recommended at this time but it is around 2 months). There is a window period that is a period of time between the time you were exposed (such as if when you shared a dirty needle) and the time that it will actually show up on the test. In other words even if you did get exposed recently such as when this happened it would take 2 months for it to show up positive on a test. So even if the test were to be negative tomorrow that doesn't mean you are in the clear..just means you weren't already exposed sometime in the past. And even if it were negative but you actually have been exposed then you can still pass it to someone else. Same goes for her. Just because she thinks she doesn't have it because say she was tested last month and it was negative does not mean she couldn't have had sex with someone or shared a dirty needle with someone 3 weeks ago (or anytime in the past several months) and now. Is HIV+ and could spread it to you. Same thing with you. If she DID pass it to you, you go tomorrow and get tested and you say whew, its negative and I'm ok doesn't mean you are. To be sure you will have to be tested again in 2 or 3 months once it has time to show up on the test...and just remember you would be able to pass it to someone else during that time period also.
I'm not trying to make you worry or feel bad but damn, you need to be more worried!! It will keep you from doing really stupid stuff like sharing dirty needles especially with promiscuous people (or anybody for that matter!). Is it really worth your life?
edit:Znegative beat me to it 
