advice? pregnancy scares?? paranoid??

Every single month since I have began to have sex (this may be TMI but this has only been for around 4/5 months) I constantly become paranoid about the possibility that I'm somehow pregnant; me and my boyfriend use both condoms and he ensures he pulls out each time (once again sorry about TMI , I just know that's important to add)
 every month something happens to make me freak out , last month my period came late , this month it ended early , and now I have dull throbbing like cramps in my stomach and I'm freaking out (I've had a bad stomach for days as well, which is another reason I'm freaking out , after my period being odd) 
Basically I'm quite young, I don't have experience with sex and stuff I can't lie and I just need advice from woman who can reasure me , because the internet worried me more , my dull cramps came up as a "early pregnancy sign " online and I felt here was a better place to seek help and reassurance 
I'm sorry for being stupid I just don't know where else to go .. :) , thank you