I cannot lift heavy on an empty stomach either. Same story as not on the rug and sbhikes... I just feel weaker, kinda offbalance. However, I eat lunch at 1 and work out after work, so I avoid that pretty easily. I also drink milk while I work out, in addition to a PWO meal.
Also, post workout is prime protein uptake time. But I think a lot of the guidelines out there about amounts and doing it within a certain timeframe are overblown. Just eat some protein and you should be fine.