Baby not sleeping as well as he uses to

So my son is almost a year old, and he is waking 3-4 times a night. It's getting very stressful, and my SO and I are exhausted. When he was 5-8 months old, he would sleep straight through the night from about 7 at night to 7 am. Now he rarely ever goes to bed before 10 pm. I've tried avoiding his afternoon nap to reset his bedtime to an earlier time, but he gets SO sleepy and falls asleep anywhere between 5 and 6 pm and there's nothing I can do that will keep him awake. I've also tried keeping him up in the morning a little later so he doesn't NEED an afternoon nap, but if he sleeps to 1 to 2 pm, he will easily stay awake until 10 or 11. Please help me, I'm at my wits end here.