Mine never became more frequent, but were extended 1-2 days longer. What I noticed was that they were very, very heavy... like, I should buy stock in tampon companies... I started maintenance in December of last year and they are still very, very heavy for the first 3 days, then lighter for the other 4. Yes, I still have 7 days of TOM since I started IP.
I've spoken with friends who also did IP and they all have similar issues, even after being in maintenance for some time.