Your pot is fine. If you turn the pot so the tree is upright it will grow much better.

Do you fertilize it?

Yes, with Foliage Pro, every time I water it. We have jut moved to this new apartment where it’s getting more light. We were in a darker place before

Do I need to change the soil? It’s been in that one for over a year

I'm using a 5-1-1 blend with reptibark and am finding out upon repots that I'm getting much more breakdown than I expected after as little as a year. You may want to have the soil stuff on hand at least if you decide to pull it out and look at the roots one day. I'm actually considering repotting with fresh soil after I'm done summering the plants outside as a new practice in fall after neeming etc..

I got 2 Cubic foot Pine bark mulch for $3.00. I picked out the pieces that were larger than a 1/2 inch and broke them up in hand. It was a lot faster than screening. I used 3 gallons of this bark with 2 gallons of home made compost with 1 gallon of Perlite to get 5 gallons for my Meiwa kumquat trees from seed. Nothing to scientific and dirt cheap.

Steve