Are you breastfeeding? This happened to me after my 2nd, my periods didn't return until he was about 15 months, and then they were kind of irregular when they never had been before. I had a very late one, took pregnancy test and got a negative. Got my period a couple days later. Could just be hormonal fluctuations due to breastfeeding or other bodily changes. Hang in there. Anything else concerning, though, you can always check with your doctor.
Things that affect our period: changes in routine, illness, stress, gaining or losing weight, new exercise routines, thyroid issues, a blip out of nowhere with our hormones. All normal and most women have occasional long cycles or missing periods. good luck