Menstrual cycle normally 28 days even after childbirth in june it went back to normal however for the last 3 months my cycle has been up to 35 days long and periods slightly shorter, why could this b?

Good question! Could be many things, dysfunctional bleeding needs to be evaluated. Hormones, incomplete shedding of the lining of the uterus, ectopic pregnancy, fibroids, overgrowth of the lining... The list is quite long, and you should be seen. Good luck!
Irreg cycles. Possibly a normal variation, but could be due to weight changes, thyroid or other hormone issues. Likely not a huge problem.