Whats going on?

So my period started just 19 days after my last months one finished, it started off with spottinf but then red blood a day later, it is muchhhh lighter than usual and what im mostly shocked about is i'm not in pain!!! 🤔 =s Shocking for me because normally im in ALOTttt of pain. Do feel worried. I did a pregnancy test yday, BFN unfortunately. Any ideas as to why my period is lighter and pain free? Trying not to stress but cant help it.