Irregular period?

How long did it take for you ladies to get a regular period after giving birth? I got my first period after her about 2.5 months after delivery and it’s been only semi regular. January would be my fourth period but I’m currently 3 days late but have had off and on cramps and lower back pain for the last 5-6 days. I’m kind of getting concerned that I’m actually pregnant again but I don’t want to test until Friday (I’ll be 5 days late which will be abnormal even for my semi irregular periods). I also had about 3-4 days where I had brown bleeding that actually got pretty heavy a couple weeks ago.