Pinpointing 1st day of cycle

After both LETZ my period got really long 7 days plus 2-3 brown discharge before and after. MRI done in Aug 2019 mentioned possibility of polyp, but multiple ultrasounds show nothing. Hospital doc put me on Yasmin to help with bad periods. I started taking it on the 1st day of bleeding (after 2-3days of brown discharge). But have to stop after 12th day due to bad cramps and lots of bleeding. I was prescribed Levest now and was told to take it on the 1st day of spotting. I started seeing brown discharge on 25th day of the cycle and I am taking pills now. Slightly worried if I'm doing it right as my periods are funny. Can anyone reassure me please?