Not getting my period anymore

So, I had my first period when i was in 6th grade (age 12). My periods have been very irregular as time passed (my bleeding lasted more than a week) and i thought it was normal since my mom’s periods are irregular as well. however, i’m now 15 and i haven’t been seeing blood during my periods. it’s just been dark discharge. i’ve never had sex before and i’m very concerned. Does anyone know what’s going on?

also i get symptoms of being on your period like mood swings and cramps in my lower abdomen.