Ay, kakaibang timing talaga when you start mix feeding, a few of us went through the same thing and our periods came back super irregular pa, sometimes longer din, especially during breastfeeding pa. Since it's been 2 weeks na at ang taggal-taggal nito, plus you had a really heavy postpartum bleed na 1.5 months after delivery, I'd really suggest checking with your OB just to be safe, sometimes hormones take time to settle back, pero better peace of mind na lang, lalo na if nag-worry ka na. Hopefully it's just your body adjusting pa sa mix feeding, pero let your doctor confirm na okay lang lahat!