UKCAT

I am finding QR and DA very difficult and have practiced but my score remains the same, I have under 3 weeks until my test and do not know what to do. I use Medify and Kaplan and dont know whether to start using the 1250Q book

If you have the book, then I'd use it.
It is much more difficult than the actual test but it will push you.
The only advice I can really give is to keep on practicing, you will eventually start to improve. Maybe try and pinpoint if it is particular questions which you consistently get wrong and practice those ones.
Make notes as to where you've gone wrong in your thinking-it may help for future questions

3 weeks is more than enough time to see significant improvements, trust me. So just keep doing regular practice every day, I highly recommend medify for it if you're not using it already! And if you are unsure about the theory then get a medic mind subscription which gives you quite good video tutorials.
For QR just keep practicing really and it will get easier, plus anything they make you do in practice is much harder than the real exam so don't get too disheartened by those scores now. The same goes for AR.
DM I suggest just think of them as puzzles and games and they seem much more enjoyable to do. Always try to jot down diagrams or charts for that one even if sometime you don't think it's necessary. Really helps!