GIRL ISSUES! PERIODHELP ASAP GIRLS ONLY!!!!:(?

okk so i just turned 14! a month ago.. and ive missed 3 periods but my periods sometimes irregular! likee i get it i miss it thean get it than get than miss it and soo on.... andd like iv missed it for 3 monthes now!? andd i dunnoo if this has anything to do with it! but i think my brother jacks off! witch is grose and nasty! soo please help and ya ! imm soo worried oh and i cant see a doctor no insurrance.. oh im a virgin 100% but member about my brother he doesnt on toilet and in shower! kk thanks help asap!!!!