Oo totoo yan, sis! A lot of us nursing moms experience super irregular periods pa rin kahit bumalik na, kaya hindi ka lang, ang progesterone from breastfeeding talaga affects your cycle pa din even after na-resume na. Since you're a week delayed now, I'd suggest checking with your OB lang para ma-rule out kahit anong iba, especially if this keeps happening, pero stress and breastfeeding can definitely mess with your timing pa. One of my mum friends was irregular for almost a year pa rin after menstruating, so patience lang with your body!