J.G.
I did experience irregular cycles while breastfeeding. Even while breastfeeding exclusively, I still ovulated, too! If you really want to understand what's happening with your body, I would start charting your temperatures in the morning. I have been using fertilityfriend.com since I began trying for my first pregnancy in 2004, and I still use it, one miscarriage and 4 children later. It's been different with each one; I don't think you're necessarily pregnant, though it's definitely a possibility. I'm not sure if your period could be affected by your diet.
I actually got pregnant with my 2nd, 3rd, and 4th while still breastfeeding the one before, and I remember having my first period at different times with each, and some anovulatory cycles, both shorter and longer than usual. My cycle never got a chance to get "regular" again after my first 2 since they were 6 months and 5 months when the next one was conceived. With them (even though I was ONLY breastfeeding, and doing it on demand), I got my first periods at 8 weeks, and 6 weeks, which were anovulatory cycles. My first ovulations after that were at 4 months and 2 months, and then I got pregnant on the next ovulation after each, though there were other cycles in between. After my 3rd, I didn't get a period until he was almost 8 months, and then BAM, they were regular. I got pregnant when he was 11 months.