first period after delivery

Giovanna
Hello Ladies.
So I am 10 week PP and last week already got my first period. I am concern because I was told when you breastfeed you don't get your period (my LO is EBF). Is that normal? 
Also after getting my period my milk supply is lower, can this be related to my period? If so what can I do to help my body produce more milk? I really want to keep breastfeeding mi LO but the way is going is getting harder because she eats 4 oz every 3 hrs on the clock and I am barely pumping 3 or 4 oz (in an hr). 
Please help me! TIA