Strange periods since TTC?!

Penny

Hi all, has anyone noticed that since TTC their periods have completely changed?! For the last 4 months I have had three/four days spotting 15 days after my last period, then my period begins. This means that my periods are now approx 18 days after my last one. Before TTC I never had spotting and my periods were every 28 days, does anyone know why this is? I have not been on birth control so it isn’t to do with that. Thank you!!xx