Hello, and welcome to the Forums! First, what a lovely picture of you and Biwi!
You're experiencing a more common issue than most people talk about. It happens. You may or may not be able to stop it, and that's okay, but there's things you can do to hopefully tone it down. Aside from a bit of potential frustration, he's not hurting himself. We have several members whose birds are chronic masturbators. Some folks provide a stuffy or favorite toy for the purpose and leave them to have their way with it when they feel the need. Better that than you, your hand, shoulder, etc., right? There definitely are times of the year that hormonal behavior is elevated. Ekkies are more opportunistic maters, so season means less to them than other species.
That said, a few things that might help...
Sleep. At least 12+ hours of dark, undisturbed sleep, on a regular schedule every night.
Diet. Reduce or eliminate sugary foods. They don't need them, or the calories, and the sugar can be a huge hormone trigger. My guy gets his veggies, but I don't give him fruits for that reason. Also, corn can be an issue for him too. It's actually pretty high in sugar, and more than a few pieces throws off the balance of things and he'll start toe tapping. I've found that dark purple grapes and blueberries have the same affect on him, so they're off his list.
Otherwise, just generally not encouraging the behavior. If he starts with you, put him down on a perch or back of a chair and walk away. Every time. Consistency is key. If he's seeking your attention, he'll learn that he won't get it by behaving that way with you.
Hope this helps, or at least provides a little insight for you