No improvements in 50m freestyle :<

Hello! I´m from Germany 25 years old and I hope my english is understandable... :) I´m swimming for 3 years now, and I really love it and want to be as good as i can! For the last year i started practicing very hard. 5-7 times a week, but i have the problem that i dont see any improvements in the 50m of any stroke... I dont have a Trainer, and there are no forums like this in german where i could ask someone. at the moment i´m swimming with someone i know from university (but he is a much better swimmer than me, 25.2s on 50m) but he doesnt know how to help either, hes just telling me to keep training^^ thats what i will do anyway!! Maybe someone has experienced a similiar problem and knows how to fix it. i will try to explain where the problems in my swimming skills are... when i started swimming and learned the techniques by myself, watchning youtube videos and reading a lot of books about swimming i have been improving very fast until i swim ~30s on 50m short course. that was about 1,5years after i started. about half a year later i was down to 28.8s on 50m short course, but from this point on wasnt improving anymore. that 28.8 is still my best time... last weekend i swam 30.1 on 50m long course. i dont understand it because i put so much effort in my swimming training, and i got better i.e. in holding good times in intervalls, or in 100m and 200m and longer distances. but no improvement in 50m. i believe i´m naturally a sprinter, i always was, in evry sport i did, canoeing, and bicycling which i first did on the street but then changed to velodrome. still i love swimming more than any other sport i did. that 30.1 makes me kind of upset... so that i want to train even harder >.