I went through a similar period during my candidature... it's rough - you can spend months stuck on some problem without some other problem to work on. You can feel like you're doing nothing more than shuffling around commas in a paper (not doing any "real mathematics"), usually not knowing how important your work is (and therefore assuming it's not very important).

My advice is to get out and about, try to get to some conferences etc. and find people who are interested in similar problems. Give lots of talks -- if there's no way to give regular seminars already, then make it happen yourself. Talk to people at nearby unis about giving talks there too. Go through the SpringerLink etc. websites and sign up to receive emails of the tables of contents of related journals.

Perseverance and hard-work will get you there in the end.