Tubal done, now late every month.

Hi,
I had my tubal done shortly after my little girl was born. She is 3 years old now. For 2 years and 5 months, my period was on time. I was never late. Exactly 28 days apart. Jan of 2011, I started exercising again, to make myself healthy. But I was late by nearly 2 weeks. Ever since then I have been starting later and later in the month. Between 29 and 32 days apart so far.
Could I have a medical problem? Or is there something else that's wrong?
Can anyone help me out here? Thank you.

[Clysta]

Are you still exercising? A change in your activity can cause you to have irregular or late cycles. If you changed your eating habits as well, it also can throw your cycle off. Depending on your age, it's possible your body could be going into perimenopause as well. This usually doesn't happen till your mid to late 30's, early 40's however. If you're younger than this, you're probably not having this issue. It's also possible you could have developed a medical issue as well, but a doctor would have to determine tests to see if that might be an issue or not.

[areno7306]

I am only 26. I will be 27 at the end of the year.
I stopped my exercising to see if that was the problem, but its still off.
My eating habits have been the same all year. Mainly fruits and veggies with some protein and fiber. But when I was cutting out carbs last year, it didn't affect my cycle at all.
It's just 2011 that I have had this problem.