Hi! I'm sure the majority of what I'm about to say will be the same as other posts, but also wanted to say that I know just how you feel my eldest was the same and he had bad excma around his groin!
I used to put a motherease boster in a disposable napy, NOT as size bigger as I found it leaked out of the sides and the top! I used a Bambino liner which draws the urin away from the skin and also put lots of 'sudacrem' boots aquivalnt is brill & alot cheeper!
I don't know how old ur lo is but when my ds was older and still bed wetting I was told to stop ribina from late afternoon and it did help! But may be your is too young at mo!
Good luck & thinking of you.