for the past two weeks I've been having pain

I'm a sixteen year old girl and lately I've been feeling weird but I don't know if there's anything wrong or not and I don't want to ask my mom to take me to the doctor, in case it has anything to do with the fact that I had sex for the first time a month ago, which she cannot know about. But I'm not sure if the guy was clean since I didn't really know him that well and cannot get in touch with him now.

Pretty much for the past two weeks I've been having pain all up and down my stomach, and in my lower back, but they go away after a few minutes and then come back later. I've also been having to go to the bathroom more often than usual, and I've gained 5 pounds. I don't think I'm pregnant or anything cause I got my period last month.

My stomach pains have pretty much gone away now but I'm having pains in my upper thighs and it's been a few hours and they haven't gone away. I also found out this morning that I have a large red bump, about the size of a mosquito bite on my upper back. But I'm not sure if it is a mosquito bite because when I touched it, it really hurt and kind of stung.
These things might be totally unrelated but I'm getting kind of paranoid. Do you think there's anything wrong with me?