I am also sorry I didn’t see this before!
PPI drugs, like Prevacid can def cause constipation. We used Mirilax with Landen. We were told that anywhere from 1/2 tsp to 2 tsp daily was ok when he was 4 months old and 16(ish) lbs. We ended up using 1.5 tsp per day in 1 bottle per day and that worked well. 🙂 I think Karo is digested as a sugar and probably isn’t a great idea to use daily, so I can understand why you would want to look into something better for long term usage.