I want to let you know you're not alone. My son is almost 5 and my daughter is turning 3 this weekend, and sleep in our house seems to be getting worse for some reason this season as well. Maybe it's just because we've had more colds this year then last, who knows.
My son that has always been a wonderful sleeper since we did do the CIO with him when he was 8 mo old or so. Now since he was sick in Dec./Jan with a bad cold has been waking up 2-3 times a night crying for us that he's afraid of something under his bed. (and he has always slept with a dim light on in his room, and won't let us turn it off) We have to take the flashlight out and look under his bed then of course by then we have to do a potty thing, then he goes back to sleep, It's crazy and I have no idea what to do. It's better when my husband goes in to deal with it then me. It goes quicker for him for some reason.
My daughter (almost 3) has never really slept well. We've tried CIO, she cries for 3-4 hours! I think we've figured out that if anything is bothering her (ie. runny nose, cold, ears, eczema) she just doesn't sleep well. And now she's decided that she doesn't want to sleep with a pull-up on, so she actually gets up at one point during the night, doesn't go to the bathroom all the time, but takes her diaper off, puts on underwear and new pjs, and goes back to bed, so then she ends up waking up early because she's wet her bed. Sometimes she'll wake up because she has to go to the bathroom so I think that's part of why she's waking up at this age. Kids are crazy. I keep remembering what a friend of mine told me once "it can't last forever". Although it seems like it will, it doesn't.
One last thought is napping. He might be ready to get rid of his nap and go to bed earlier. My daughter does sleep better when I can get her to bed earlier and skip her nap. But our weekday schedule doesn't allow for it as much as I'd like.
You should definitely take turns with your husband though. That will hopefully let you not be as drowsy during the day. Even if you're a SAHM that doesn't automatically make you the one that has to suffer more. You're both parents, you both made the decision to have a child. I've been a SAHM and a work outside the house mom, both are difficult. Sharing the nighttime duties I would think is something that you guys should consider.
Good Luck! I look forward to seeing what others have to say.