I've been having a very odd cycle these last few months and I'm not sure what the cause might be. I'm looking for some advice/help on the matter. I'll try and provide as much detail as I can, but if more is needed, just ask and I'll try and answer
-Very first cycle: May 2004
-What an "normal" cycle was for me before it became weird: 1day reg., 5days heavy, 1day light (7days total) every 4 weeks (week 4 being the cycle week).
-I used to play soccer and would often skip and sync up with my teammates, but its been well over a year since I played soccer.
-I moved into a dorm in Aug '07, it was an all girl's hall, I sort of synced up with my roommate, but we were never quite the same.
-October 2007 I became sexually active.
-May 2008, I moved out of the dorm and into an apartment with my (now) husband.

Anyway, the issue now:
I've been tracking my period since Dec. 23, 2007 which is sort of when the changes began. (So I had been sexually active about 2 1/2 months at this point and living in the all girls dorm for about 4months).
My Dec. period was normal as far as I could tell, the only change was 4days of heavy flow and two days of regular flow instead of the normal 5 and 1.
Then come Jan. 2008, I completely skipped my cycle.
My Next one was Feb. 14, 2008
March 23, 2008
No flow April
May 8, 2008
and none yet since then.
My flow has also changed to what is considered a "regular" or "average" flow. 2-3days reg, 2-3heavy, and 1-2days light. (still 7 days total)

I've also stopped getting any of my usual "Hey! Your period is about to come!" signs. I used to get light cramping, bloating, mood swings, fatigue, and sometimes tender breasts before my cycle and after Dec. I've gotten none of them. I get them during my cycle, but my cramps have become far worse than they used to be. I also have been experiencing cramps at random between cycles.
I've been trying to figure out what's up since this is all extremely unusual for me and it flat out sucks having it just show up...always when I'm least prepared :/ (and on two holidays!)

A friend of mine suggested that I might be out of whack because I'm sexually active now and my body hasn't adjusted. But if that's the case, why were my Oct, Nov, and Dec cycles normal but come Jan, they all changed? And when should I start to become normal again?

Another older woman I know said I might have a thyroid problem, I looked that one up to understand it better, I have some things that are considered symptoms to it, but they seemed pretty standard to other things too...

Anyone have any thoughts? Suggestions? Ideas?

I don't know if this will have any baring on any of this either, but physical attributes about myself:
5'6"
118lbs
18years old
Fairly pale skinned
Get cold very easily (I don't have much body fat)
I appear fit, but I'm a little out of shape
Love to eat, very fast metabolism

Like I said before, if you need to know anything else, I can share to the best of my abilities, I'm really just trying to find out what might be up :/

Thanks!