Many would be happy to reach 1400. Some players plateau out. That could be your maximum.
What do you mean you "know about pawn structure, positional play" ? Do you think you know all there is to know about those areas or know the basics only ? If you want to increase your chess knowledge you must read chess books too. There is much information to learn.
I have played some 5 and 10 min rapid, but I seen to be stuck at 1400s, can anyone better than me help me? I already know about pawn structure, positional play, but I'm still stuck.