Tima84, Have you got flightsim? check out vatsim on google and try get on flightsim flying online, there you can pick up a bit of atc knowledge, you could do an R/T course too.
secondly, i know your instructor is trying to help and hes telling you what he thinks, but ask yourself if hes the right instructor for you. when your low on confidence and he tells you that your slow and the biggest challenge, will that really help you?
Im in Florida at the minute, at first I found it slightly hard to grasp the way my instructor taught me, it felt like he wasnt really guiding me in the way i expected. Then I had a change of instructor cos he the other guy was off. I settled right down and he helped me understand my errors and taught me through the steps. Im now back with the original guy, who is the CFI, he has fine tuned my ability, if you like, and I feel fine with him now. I can tell sometimes hes not impressed, but he wont tell me, in fact today I did a Prog check and thought I did crap, I expected him to tell me so, but he said I could bust you but I wont as I know you can improe it next time. Thats what instructors should do, he knew my confidence was at breaking point but he kept me up, hell never tell me Im bad, hell just tell me we learn it till you know it, and what ever you spend, you spend. Just remember, and this goes to anyone with money doubts or doubts about taking longer than others, another lesson to 'fine tune' something may cost more money, but you want to be a safe and effiecient pilot, you have to learn the basics and get them right. Theres no point half accepting something and moving on if youll only fail at it later.
Good luck