Hi Emma,
How old is your lo?
The DF does not always work for every lo, it can end up causing more NW's for some lo's. How long have you been doing the DF for now?
It sounds like your lo is having difficult transitioning into the next stage of sleep. Have you tried staying in the room when your lo naps, and when you see him starting to stir, you can pat / shhh to help him get into the next stage of sleep?
Can you post what your day is currently looking like:-
E - breast / bottle - how long
A - how long
S - how long including wind down routine and needing to be re-settled.