Most likely one of two things:
1) you are not counteracting (eliminating) current drag and therefore the fish never see your flies properly (slow enough or long enough). Just because you have an indicator does not mean you fish it and not the flies--far too many novices make this mistake.
or
2) there is too much slop between your indicator and flies and you are just not seeing the takes.
A mentor is invaluable to any fly angler!