Could I have a mental illness?

i have just been watchin this programme on tv and it has got me wondering. when i was 14 i took an overdose but it just made me sick, i have self harmed loaded and tried to hide it from everyone, now i have really bad mood swings and panic. i hit my head up the wall and go mental and scream at my bf and go crazy when we fall out it can get realy out of hand ( if i was an on looker i would think i was mentally ill) then i can go normal again, i have wondered for ages but always blanked it now after watching this programme i am wondering, i am 18 by the way.