Try goat's milk. Our daughter had a dairy allergy from birth with GI issues-rashes-reflux-bad sleep, but nursed and was also on Elecare until about 13-14 months (I have a dairy allergy and even had to abstain from goat's milk products while nursing). We like the Meyenberg brand.
The the allergist told us she tested clear for regular cow dairy at 12 months. But it went hideously bad in just a couple of days with fitful sleep, gritty bloody stools and rashes. Went back to formula. Started her on a probiotic (a non-dairy gel-capsule variety from the cold case in Whole Foods vitamin section) added into her formula for a month and gradually began to add a little goats milk at a time over the next month, and she did fine. Now she's just on goat's milk and still does poorly on anything with cow's milk in it. Even a few cheesy crackers cause terrible gastric distress and awful diaper rash.
The pediatrician said that the immunity in the blood and the immunity in the GI tract are sort of separate, and that even though she tested OK with the stick test for milk, that doesn't mean her GI tract had caught up yet.
Digestion slows down to a crawl and practically stops at night when you sleep, so anything that can irritate your guts spends a much longer period of time sitting or moving through there.
As far as constipation goes, I just make sure she's hydrated enough during the day, and try individually packaged prunes or prune juice mixed with apple juice (or prune baby food when she was about a year old) only in the morning. I found the reflux medication seemed to cause more problems than it fixed, so I took her off of it.