stress n lack of sleep will reduce your milk supply. i have the same prob n stress as you. so right fr start, i told my hubby that i wont hesitate to give formula milk if i dont have enough breast milk for him. till now i'm still giving him mixture of fm n breast milk.
in my opinion, if you r really too exhausted, cant give breast milk, then give him fm. most impt is baby have enough to drink.
dont stress yourself too much 'cause it'll only lower the supply. take it easy ya!