You certainly have given it enough time. There is a couple things to try I can think of. Easiest is to take each bottle turn it upside down to mix in the yeast and priming sugar again, put them back upright and wait some more. That works sometimes. I imagine at this point you are sick of waiting.
That’s a big beer. The yeast may be stressed from all that work so, it will be a pain but you can get some dry yeast, uncap each bottle and sprinkle in a few grains then re-cap. Then of course wait again.
I have to agree with @uncdeo I would not ove gone with the fizz drops. There have been other complaints about under carbonation with them but how would you know without trying them. Could add a little table sugar with the yeast but how much will be the question. Too much and boom! Bottle bombs.