Questioning? Looking for tips

Arielle
I don't post often, but I wanted some  advice and some help. Ok, so here I go. 
My period sometimes comes late and it varys on how late, sometimes it's a few days, sometimes it's weeks. A few times I have taken pregnancy tests and they aways come out negative. Are there other reasons why my period might be late. 
I'm 5'2" and I weigh 120.2, I eat very healthy and I exercise every morning.