when do females become fertile after their last cycle

Hi everyone I have been searching the internet for answers & still really no understands , so typically I get my period every month on the 23rd either early in the morning of that day or later in the day , but this month my period was late , the days leading up to my period I was discharging some milky white ish clear ish kind of discharge , then the day when my period was suppose to come , the discharge was almost like water , but was very light , then the next day later that evening I used the restroom & when I whipped I seen a dot of some brown discharge, but it wasn’t much, more like a drop , so a while after I had to use the restroom & as I whipped I seen like a pink discharge but it wasn’t much so I put tissue there , thinking maybe my period is about to come but all that night I didn’t get anymore discharge or my period & as of today I started bleeding , w mild cramps. But the days leading up to my expected period , my tits were very very sore & swollen I was suffering from headaches that continued for days & became more intense w each day , then having back aches, but today they have become more severe my lower back just aches & aches but my cramps aren’t bad as they normally be on my first day of my cycle , if possible can anymore help me ? Could I be experiencing implantation bleeding ? Please help I need answers