Sometimes you can have ovulatory spotting about 2 weeks before your period. Or about a week after your period is over, if you have a "normal" 28 day cycle. (I use the term "normal" very loosely.) If this is the case, it's not a problem, although the change may well be related to weight loss.
I've always been irregular, which is why I've been trying for a baby for nearly 3 yrs with no luck.

I haven't noticed a change yet, but I'm hoping with further loss that my periods will regulate themselves.
Hope this helps!