Hi I'm At 19 Your Old Female. I Normally Have

Hi I'm at 19 your old female. I normally have heavier cycles but I haven't received my period since beginning of July. My normal cycle can be up to 50 days. I've taken 5+ pregnancy tests all different qualities and brands..negative. My boyfriend and I usually wear protection but there's been a few times we haven't but he's really good about pulling out (I've done this since My first bf about 3 years ago) and so I don't think he's ever ejaculated inside me. I've been having cramps and back pains for the last month or so, nothing too severe most of the time. No nausea or mood swings or anything like that either. I will be honest, I started smoking marijuana more frequently since about May/June and I've heard that can effect your menstrual cycle..? I've also noticed my legs have lost circulation easier (falls asleep quicker, etc.) mostly my left, not sure if in correlation though. Today and yesterday (a few days after I was supposed to get my sept. Period) and around when I was supposed to get my period last month I've had like a light brown/grayish/reddish discharge, lasts about half hour very slight and it's gone.. Any idea what it could be? I haven't had any money to go to a doctor yet so I kind of just want to know what I might be expecting..