Hi there, thank you for sharing your composition! Here are some general comments:
Movement 1 - I think the main thing I enjoyed about this was how bold it is compositionally. I really enjoyed reading your story of getting into composing through doing theory exercises. I'm confident studying theory will continue to enhance your compositional skills going forward. There were a lot of very nice moments throughout this movement. To my ear, the opening melody (in measure 2), when it drops down to the low F, it just feels a little odd and unconvincing. Of course, as everyone will tell you, write what you want to write and what sounds good to you. But also, listen carefully to your music and try to distance yourself from the fact that you composed it. Ask yourself, "Does this really sound like I want it to, or could I make a small adjustment to rhythm, melodic contour, or harmony that would bring it even closer to what I want?" It's a real struggle to have this mindset (speaking from experience), but it's worth it when your piece begins improving right before your eyes!
Movement 2 - I really like the connectivity of this movement. The times when the piano begins a melodic line as the cello ends one are truly lovely. The dramatic pause in measure 40 (+ the measures leading up to it) is very effective, as well. The delayed piano chords in measures 50-52 are great! I would also delay the big Bb Major chord in measure 53, as having it on the down beat is almost anticlimactic after the excitement of the previous measures.
Movement 3 - This is a very exciting sounding movement, and it definitely contrasts the first two. My favorite moment is at measure 105 with that staccato piano line under the legato cello melody; it's a very cool effect.
Overall, great job. For being your first composition, I think it is incredible that you composed a whole, three movement sonata. I have no criticism for it. I would suggest that you listen to a lot of music from different styles and composers. I think this piece may have some moments where it isn't very clear where the points of arrival are, or what the "direction" of the music is. There is certainly nothing wrong with writing music that is more ambiguous to listen to, but I just wanted to say it did strike me as being a little bit on the "wandering" side (as opposed to the other extreme, which would be "Point A very clearly goes to Point B"). Again, great job, and best wishes!