Birth control?

Curious after you start taking the birth control pill, how long do you start feeling changes or side effects?? Or how long does it take when you start noticing a difference, im on a low dose estorgen pill called microgestin fe 1/20 btw. But just curious, i start taking it tomorrow morning and im so nervous plus im almost 3 weeks pp, i even was going to ask is it ok to start it even if i havent got my period yet or should i wait till after im 6 weeks pp to take it. But doctor said i could start taking it now plus i want to start taking it and see what happens so when my 6 week checkup comes up itll be 3 weeks for me taking it and if i have issues i can always try something different and let my doc know...

Advice please!!!