Twosetters I need some help

So my main instrument is piano and I enjoy it a lot, but I also play cello. I started playing for school but my problem is lack of motivation. I can’t find a reason to practice everyday. The school music is impossibly easy so we bought a couple of Suzuki books (I’m somewhere in the beginning-ish-middle of the second) but I don’t feel like I’m improving. I don’t even how if my technique is correct. Do you have any advice?

Edit: sorry I forgot to say I can’t get a teacher