You should have it checked out. Bumps are caused by many things, most of which are not std related. But unprotected sex with someone who has had sex before is still a risk. So, even if for peace of mind, you should go to a doctor and have it looked at.
Don't sound good. I hope guys will advice you better. I just know it may be std; i had had similar pimple at my labia 3 years ago; still now I am not sure what is the cause. I am almost sure that I am infected with HSV2 (but doctor didn't want to make test); while I am not sure if HSV2 can cause such pimples. Perhapes is something else. Somethimes "devil have more kids" by the same time.
So people: try to be honest and stable in relationships!