Ok, the problem is the millet. Millet is a treet, not a food group. You should be offering pellet and seed around the clock. An only seed diet is NOT healthy for a Lovebird in any shape, way, or form. You should also be offering fresh fruits and veggies.
As long as you see him eating, it's completely normal for them to start stepping away from the formula. Make sure you keep offering feedings until he excepts no more then 1 or 2 cc's. This is very important, I've had chicks revert when I've thought they were weaned and I had to go back and do a couple more days. You really don't want the bird off formula completely until mid week 7.