I don't have advice per se but I am in the same boat. It's almost like reading exactly what's going on in our house! My 5-month-old son was a great sleeper from the start- typically only waking up 1x/night for feeding. Now, he is waking up several times a night. I, too, am doing a DF at 10 pm and he is waking up b/w 1-2 am for another feed and then back up again around 5 am. He is guzzling his bottles in the middle of the night which I'm worried is contributing to the problem (meaning, that he is getting more nutrients in the middle of the night when he really needs to be getting those during the day).
I should note that he's in daycare M-F so much of his schedule is not entirely in my control. I encourage them to put him down around 9 am for 1st nap, 12-1 pm for 2nd nap, and then he usually naps a little once I get him home. I put him down at 6:45/7:00 pm.
I do think he's teething but I don't remember having this hard of a time with my firstborn!