Mine did the same did the same thing, my hair is curly and it dreaded up so fast in the back my roots got tight, so far i have just allowed them to grow some which has helped, dreads are ever changing so they have loosened and tightened and loosened again etc.
If one or two single hairs are tugging its usually because they dont "belong" in that one dread so i separate them out. And found a way to sleep without any tugging, (for me moving them all in one direction did the trick.)
I also avoid rubbing too much (such as while washing) so that im not making more knots form to fast.
Letting my hair get a bit more "dirty" and therefore a tiny bit more natural oils being in the hair helps a little too.
Hope you can find a solution!