Need some advice!

I'm not good with keeping track of my periods. So I have been using the app to help. So hear is where I need help... When my period is suppose to start it is usually very light to where I don't need a tampon and that will last a couple days then it will be heavy for a day and half where I'm changing my tampon every couple of hours. Then it's over well at least I thought. Then after having sex with my SO I was bleeding again after and the next day.  I'm not sure what's going on and on the light days I should count that as my period or spotting?