Sleep

My little guy had gone through his sleep regression for several weeks and around 19 1/2 weeks he started sleeping normally again. He sleep anywhere from 6-8 hours for this first stretch and then smaller stretches after. Anyway he's now 21 weeks and it seems like we are going through wave #2 of this thing, it's been 4 days of no sleep again. It's it normal for the regression to have a good period? He also just recently mastered rolling from his back to his belly a few days ago, could this be the cause?