I agree that it is probably temporary, and should be better tomorrow. But if not, it's possible that you have been scratched and have an infection. Does your girlfriend wash her hands before you two engage in this kind of thing? If not, just like you being responsible to tell her it's uncomfortable, you are also responsible to be sure of hygiene. You're not the passive recipient of others' actions, but are the guardian of your own sexual health.
Saying you won't go to the doctor because you need to ask your brother for money and don't want to, is kind of silly, by the way. You don't have to tell him the exact reason you need to see the doctor. There are a lot of things a woman sees an ob/gyn about that wouldn't cause questions -- a UTI, a yeast infection, aching with periods, things like that. If your brother demands to know what is wrong before he will pay for a doctor appointment, that is just weird, but if he does you could give him one of those explanations and he'd probably be too squeamish to ask further.
You need to tell your girlfriend when it is uncomfortable. It's NOT supposed to be. Friction and this type of thing can cause swelling. You can throw an ice pack on it (bag of frozen vegi's?) and it will go down. I don't think you need to go to the doctor at this point. It should go down in a day.