Big, big hugs . You aren't doing anything wrong! Your DS is 4 months old and this age is notorious for constant wake ups! Their sleep patterns change at 4 months and they tend to need some more help getting back to sleep. If you Google "4 month sleep regression" you will find you are not alone.

I went through it with all of my babies at the same age, it was so hard at the time, but it did pass.

More hugs , you will get through this