I used to so regular.....?

now I don't know what is going on with my body. For years my cycles were 31 days long and I got pregnant with my first on cd15. My periods came back to normal even before I quit feeding and as before, came on every 31st day. My baby is 8 1/2 months and now I am all out of whack. For 3 mos now they have been shorter (26-27 days) and I would still O at about the same time (bbt), at about cd 15 or 16. This last period came at cd 23 and the bleeding lasted 10 days! Much heavier and with lots of clotts. I am on cd 19 and still no raise in temp to show that I have Oed. I am an otherwise healthy person and my eating and excercise patterns are as well. This also helps with the stress of my fast pased career. Since those have been consistant for several years, what on earth is making my cycles so crazy??? My Dr.'s nurse told me to chart and keep tabs on my cycles and come in if it continues for a few more months. I don't want to wait. Help??!??!?