I have low thyroid and have been on new medicine to get my thyroid to normal level. And the medicine has made my periods very regualr as to before I was having one every two or three months. So I start on the 14th every month. My husband and I had sex on the 14th since i had not started my period and he ejaculated in me and my period didn't start till the 15th. I had cramps and tender breasts and PMS and usual flow of bleeding. But its very brown and today is the third day and its extremely light like my period is about to be over which is not normal for me since it always last 5-7 days now. Is this implantation bleeding or just a normal period?? We would love a baby and have talked about stating to try soon so this would be wonderful!!