So, if I have your timeline right- you fooled around with your friend when you were ten years old, correct? That seems to be an age at which your friend would have been very unlikely to have had anywhere near enough sexual experience to have contracted anything passable to you.
Assuming that your friend DID have something though (keep in mind, I don't think he did), oral sex is low risk for transmission of most STDs. I seriously doubt you contracted anything. Considering a) you were only ten, and presumably, your friend was as well, b) I don't know of any STD that presents itself after a month, then sticks around for four years without changing- I really think you are fine. Herpes would have presented as a series of small, painful blisters that eventually would have crusted over; and genital warts would not have presented after only a month (and are VERY unlikely to have been spread via oral sex).
If I had to guess, I would imagine that being the age you are, your body was undergoing some serious changes (the genital area has a number of bumps on it that develop during puberty... hair follicles become more pronounced, oil glands, etc.) and that your shame associated with the event has made you sensitive to STD issues.
I really don't think you should worry about STDs. If you want to get checked out, by all means, do, but I am pretty confident that all the tests will come back just fine.
I agree with tommerhawk. That's probably the best thing you could do.. You should hold off on doing anything with your gf bc you wouldn't want her to have it. try not to be ashamed to get help.. I know its easier said than done but in your defense you were only experimenting.
got to a clinic get tested tell a doctor about your situation he or she will respect your privacy and will tell which test you need cheers