Test is negative, my period is brown, I've noticed rapid weight gain

This June I Had Missed My Period I Had Unprotected Sex Around The Time My Period Was Post To Start. Going Into July I Spotted Then Few Days Spotted Again But No Period. Going In To August I Had My Period brown not any where near bright red or red like my regular period . now going into September I had no period again I Dont Know Why IT keeps Doing This I Fell The Same But I've Noticed Rapid Weight Gain And Change Of Behavior (hothead ,emotional ) I've Took Pregnancy Test All Negative. No signs of pregnancy .its now October Felt A Pain Yesterday kinda crampy sharp . woke up this morning with 1 tiny spot of blood . I'm 18 And My Mom Never Has The Time To Care For Me And Take Me To A Dr So I'm Just Sitting Here Afraid That Something Is Wrong With Me.