What Causes Scanty Period Followed By Non Stop Periods With Headaches?

i was not having my periods or rather very scanty periods for 2 months. i did a pregnancy test and it was negative but abt 8 days back i got my periods, but now it is not stopping. for couple of days i get excrutiating head ache in the night due to which i wake up.. but then it comes down after a while.. my normal days of periods are 3-5 days ... but for past couple of months it is going haywire.. pls help.. oh iam 29 yr old married women.