Constipation and Cows Milk

[Anniejo91]

Hi Everyone.
My DS turned one last week, and he's been drinking cows milk for about a month. He's suffered with constipation since 9 months, and was taking 2.5ml lactulose twice a day which worked wonders. However, since going on to cows milk, the constipation came back with a vengeance. So doctor put him on movicol, one sachet a day and that seems to be working fine.
I spoke to HV today as I'm worried that he'll be on movicol forever at this rate, and she recommended that I cut out one of his bottles (he has 5oz in morning and 8oz at bedtime).
He has his bottle at 6:30pm and goes to bed at 7pm. However, he only sleeps through until 4-5am before needing his morning bottle (he then goes back to sleep until 7am). So I'm worried that if I cut out his morning bottle, he'll be so hungry that I'll have to give him his breakfast at 4am! And if I cut out his bedtime one, there's no way that he'll sleep through.
Any advice would be greatly appreciated! xx