Period shortened

Does anyone know why your period would change from being 7-8 days to all of a sudden 4days? The last 4 months my period is super short and I worried it’s something to do with my fertility? Me and hubby are infertile and have previously done <a href="https://glowing.com/glow-fertility-program">ivf</a> to get a baby. Iv got endo but apart from painful periods and ovulation there is nothing else that really is wrong.

Just curious as to reasons why your period might become short?