Ummm???? idk whats going on

So Usually my periods are like kinda heavy and then get lighter.... but in june I started bleeding on the DAY i was supposed to get my period it lasted 2 days and was brown and then light pink/red. a week later I started bleeding kind of like a normal period for 4-5 days but it was still rly light! I took plan b like in june I think and idk if it can mess with your cycle. Its been a month since he came in me and ive taken 8 tests and they are negative but my period in july was also lighter and 6 days late and lighter then usual and lasted 4-5 days, didnt have spotting. is it possible that im not pregnant but his cum messed up my cycle?? or could I be stressing out thinking i'm pregnant and thats why i've been late and lighter then usual? could it be hormones or a cycle change? help please idk whats happening