7 month old will not sleep.?

My son is 7 months old and has never slept through the night. I put him to bed at about 7 to 7:30 and he goes down awake and falls asleep on his own without crying at all. But he wakes up every 3 hours to 40 minutes. I feed him plenty during the day and breastfeed him, at night when he wakes up I nurse him but he isn't hungry and usually falls asleep very quickly, but sometimes he will be awake for up to 2 hours in the middle of the night. I've tried everything, co-sleeping and having him sleep in a crib, wearing him all the time and holding him regularly, letting him cry not letting him cry, swaddling and not swaddling, putting him to bed earlier and later, feeding him solids right before bed and doing it an hour and a half before bed, music, white noise, bedtime lotion, keeping the house warm and keeping it cooler, nursing before bed, giving a bottle of expressed breast milk before bed, several naps a day, only one nap a day. NOTHING WORKS!!! He has never woken up less than twice in an 8 hour period, but its usually 4 or 5 times in 12 hours. The reason I feel some urgency in resolving this problem is because I am 8 weeks pregnant with a new baby, and breastfeeding while I am pregnant takes A LOT out of my body, and I am already exhausted, not to mention that there will be another baby who needs me soon. I don't know what to do and I am so desperate for some sleep. He is a very energetic baby and is already crawling and pulling himself up to standing position in his crib and on furniture, so our days aren't mellow either. I've met so many moms with babies who have slept through the night since they were 2 1/2 to 4 months old, and hearing that makes me so jealous. I just want one good nights sleep! PLEASE HELP!