Worried sick - need reassurance

Beatrice
Hey everyone
I am freaking out. My period finished on 8th March. On 12th my boyfriend and I had sex - we used a condom as usual, but we fooled around without it a little bit at the very beginning for like, 5 seconds. 
2 nights ago I had light pink spotting that lasted maybe half an hour. It scared me half to death because I have never had it before. Naturally I started googling and learned about implantation bleeding so I started freaking out... Had no other symptoms until today when I had 1 hour of cramps like when my period is about to arrive. 
I know I wasn't in my fertile window but I keep worrying something happened?? I'm going to see the nurse tomorrow but in the meantime please can you help me to calm down? :(