Female problems. What's wrong. Help.?

Ok so I have a boyfriend we have sex regularly. I'm not on BC and so we use the pull out method no condoms. I got my period from may 13-18. 2 1/2 weeks later I began spotting and got my period again June 8-12 which was early. And shorter than usual. It is now June 25 and I am spotting again and my right breast is a bit sore on the right side of towards my underarm. And sometimes I get nauseus but not a overpowering nauseating feel it comes at very random times and and it's a very brief feeling. I never throw up I just feel a slight feeling like I need to the feeling passes fast. I know it sounds like I maybe pregnant but since my May period I took a pregnancy test and I've taken 2 in the past week all have been negative? Any answers help