
I use the same thing for both of my dogs. ;)
The older boy, he took about 6 months to get used to it fully, we also went through the stage of him "bucking", trying to paw it off, to him laying down like a lump of lard and refusing to move :rolleyes: and although tolerant of it now, I have a sneaking suspicion that he still would rather not have it.
A few weeks ago I put him back on a normal half check collar (we had temporarily lost the dogmatic) and it reminded me of why I had to find the dogmatic again

he will always be one of those dogs that has to pull, in my breed they are very often called the "leader" ie, they always have to be infront.........boy does he take it literally.
My 6 month old pup still hates it and goes into a strop when I put it on her. I did all of the breaking in gently with her, the same as I did with Murfee, but she still rebels against it.
I have been taking her out as many times a day as I can manage and in the garden too, to get her more used to it as she too has developed the tendency to rip arms out sockets

3 weeks isn't that long, if you want to continue using it, give it more time. If the alternative is Luke pulling you over then I would persist.
The reason I got one for my older boy is despite consistent training, he still pulled and one day, pulled me over. That's when I decided that I had to try something different as letting him pull me over was not only dangerous for me but as I was out of control of him it could have led to a disasterous situation that nobody needed :(
I know that there are people who don't agree with them, but for me, it makes for a calmer, happier walk and once we're 10 minutes into the walk, both seem to forget that they are wearing it :)
HTH :)