What Causes Irregularity In Periods?

I'm an 18 yr old teenage girl, normal weight, sort of healthy.My period has been very irregular the past month, it started when I had to take the morning after pill because of a broken condom. My period didn't arrive for about 3 weeks, maybe longer. It came near the beginning of December, it went on like a normal period, maybe a bit longer then normal, then for the next 2 weeks I had light spotting/brown discharge and occasionally clots coming out, then I got another period in the same month, it was light, then another two weeks passed with the light spotting/brown discharge still, the clots coming on more often, and I have my period again, and its very heavy some days, very light others and there has been very big dark clots all throughout this current period, sometimes no blood, just clots, other times heavy bleeding.

It's worrying me because I've never had my period be like this before and its been going on for so long now and I've been reading up all the possible reasons and its filling me with worry. I'm just sick of constantly having my period be there, light or heavy, what's going on?

- Also if its any help, before my first period when all this began I had a lot of stress in my life and had lost a lot of weight, hadn't eaten properly, been doing some marijuana, also a heavy smoker, I don't know if that makes a difference, I thought I would put it out there. And I'm on a gluten free diet if some sort of deficiency is causing this?

If you could help it would be greatly appreciated :) I am considering going to a doctor if this continues.