4 months pp, irregular bleeding throughout the month and after sex, lower back pain waking me in the night.

[Bethpp1]

Hi, has or is anyone else had this, first baby, i bleed the next day after sex for a few days and also bleeding every few days with breaks of 8,9,10 days in between for the month every month. Not breastfeeding, normal natural birth, no complications and good pregnancy, was on mini pill and recently swapped to another pill and still happening. Back pain wakes me up 2-3 times in the night and goes away when move around or sit up in bed for 20- 30 minutes, go back to sleep and wakes me up again after another 2-3 hours. Smear test up to date and i have blood test coming up for back pain and ultrasound for bleeding. Any insights and advice would be welcome in the meantime, thankyou.