BP suddenly turning aggressive?

I've had my BP, Nutmeg, for 4 years now- raised him since a baby and he's very tame. He let's you kiss his head, puts his face to yours and let's you squish his cheeks. Lately when feeding him, defrosted thawed rats with tongs, he's tried to lunge at me instead so I've resulted to lightly tapping his head with a pen or paper to make him back off and then he'll go for the rat. Today, however, I opened his tank to change his water, he poked his head out of his hide, went into strike stance and tried to strike me. I moved away in time, he has nipped me once while feeding though, felt like I shoved my hand into a bowl of needles. He continued trying to go for me so I again used a pen to make him back off, just by putting it infront of the hide entrance (he was in his cold hide). Is there any reason for this behavior? His tank got a deep clean last month, the humidity and temp are all perfect and he gets fed every 2 weeks. I know for his age it should be once a month but he's 200g underweight so I want him to just meet the standard. He does have 2 cockatiels as roommates but he's never acted out because of their scent and they've been roomies for a year. No I don't let him out around them. He's an an Axanthic Banana if that adds to anything.

Thanks in advance for any tips and help!