Mummies help !

Im 3 days PP tdy. Been exclusively breastfeeding since day 1. And so far, so good.. despite the every hourly demand latching, Baby has been latching well. Till both my nipples super sore and "torn". I do apply the nipple cream as and when i can but because my baby might even latch every 30mins-60mins, my nipples couldnt heal properly and thus resulted in more pain. Yesterday i realised, my both boobs gettimg engorged eventho i latch my baby often and for long each time. The engorgement doesnt seems to subside.. i wonder why.. is baby not drinking at all or...? Every 10-15mins she ask to be latched. With the pain getting even more painful, i had to feed my baby formula. My 3yrs old formula milk bcos i hadnt had the chance to buy a newborn formula yet. I feel guilty. What will happen if a newborn drinks a 3yrs old fomula milk? This is the first time i had to do this. My nipple pain is soo unbearable and baby was fussing, crying non stop asking for milk. And, what can i do now? With this nipple pain (cracked nipples) and both boobs engorgement... Pls pls advise! Urgently need help!