Birds can react differently for a number of reasons. It could be that something has spooked him and he is now scared of being handled. It could be that you have changed something about your self and are unaware of it which has frightened him. Bare with me because I don't know if you are male or female LOL! You could have changed soap, cologne or perfume, painted your nails, wear a new watch or other jewelry or be wearing a shirt with different length sleeves or of different colors. If you can't find any other signs of sickness then try to think back and see if there is anything you may have change however minor or major that could cause this problem in him.
Lastly if none of the other ideas seem to be working out it could be that he has started into his "testing" phase. Many birds no matter the size and even if they are handfed will go through a phase when weaned or during sexual maturity (many refer to it as the terrible twos although depending on the bird may start as early as a few months or as late as 10 or more years). This phase usually involves testing their caretaker. Nipping, not stepping up, puffing out feathers etc basically to see what you will put up with and to try and show you it is boss. If this is the case you must be patient and may need to start from scratch with "bribery" LOL! A favorite treat or toy may entice the bird to come to you or redirecting a bit towards a toy may help save your fingers from a few nips. If he offers to bite have a toy handy and direct the bite toward the toy while offering the other hand to step up on. Keep the toy handy for further bites.