Expressing milk and having postpartum period/bleeding twice in a month

Hi mummies As my baby is still in the hospital since he was a preemie, I've been exclusively expressing milk (not doing breastfeeding at all due to his condition). I then experienced bleeding on the 10th week postpartum. It lasted for 4 days with light flow. Then, the bleeding came back 2 weeks later with a bit heavier flow. Is it normal? Is this period?