Actually, nearly all Planned Parenthoods do do testing, that's part of what they're there for. And most have a sliding scale. So, rather than make yourself nuts with worry, all you need to do is pick up the phone and call to find out.
Even inb the off-chance they don't, they will be able, no doubt, to refer you to a handful of local clinics. Let them know you need a GYN exam, and a full STD and STI screen and that no-cost or low-cost is vital.
Just a few thoughts for you: "virginity" isn't a technical term, it's a cultural one. And while not having any sexual partners offers some protection, it doesn't offer all. To boot, as a rape victim, I do hope you have it clear in your mind that one doesn't make a choice to be raped. It's terrible it happens but it does, and when it does, the best any of us can do is to take care of ourselves physically and emotionally the best we can. if you didn't get good counseling or support after your rape, I'd suggest you seek it out. Really, it can make a world of difference, and some of your tone says to me that you could use it.
In addition, you get to make your sexual choices from here on in. If you wish to be celibate for a while, you certainly can be. That is completely up to you and whatever is best for you is beyond fine. Seems like you need to take some time to figure out what you need.
Lastly, while you need tests to determine what's going on, it is possible that both these issues -- the sore and the menstrual irregularity -- are benign. You sound pretty strezzed to me, and that in and of itself can create irregularity. That sore also could be a benign cyst or indeed, a deeply ingorwn hair. So, try and relax a bit before you can get that appointment. While only there can you find out what's up, being this scared and stressed isn't good for your health, either.
Hang in there.
Editor and Founder, Scarleteen
My epitaph should read: "She worked herself into this ground."
-- Kay Bailey Hutchinson