Betta Fish: Betta is frantic and vibrates..? (help)

I got my little guy Oscar November 1st. It’s a 5.5 gallon tank, heated consistently at 78 degrees, nice sponge filter with no excessive aeration, and decently planted. He eats normally and I don’t see anything really wrong. He is my first fish. 0/0/5 for ammonia, nitrites, and nitrates, I check twice daily. Light is on only 8 hrs a day. Water changes every other day as I’m doing a fish-in cycle w/Tetra Safestart Plus.

Here is the problem: Oscar flares at himself on all sides of the tank and headbutts it. I didn’t get it on video but he acts like he nods yes or no very frantically, and he even looks to be vibrating when up close to the glass. He can do this for 8 hours straight with breaks in between. Can someone give me advice on what to do? I think he is really stressed out and I feel terrible. If I have to rehome him I will with no hesitation, I don’t want to fail him 🙁