Hard to tell, but it looks to me like something is connecting to a point on the inside or other side or is unintentionally overlapped in a way that messes up the faces (not the right number of vertexes). It’s possible that adding a vertex or cutting a face might fix it, but I don’t know. I found 3-D modeling very difficult because things like that kept happening and weren’t easy to fix, although other people seem to have no trouble with it.
For gesture, one of the ways I was taught was to practice by tracing pictures (photos and/or comics) not entirely but just a few key pose points: approximate spine line (as a curve), ellipses for shoulders, elbows, and wrists, hips, knees, and ankles. Then taking the picture away, with just that spine line and those 6 ellipses (possibly moving a couple to alter the arms/legs, stretching or condensing), flesh out the figure, being careful about balance and that spine curve. It helped me improve somewhat at least.
I’m no good at expressions, so I sought out someone who was and they suggested I practice using something that exaggerates expression, like anime or caricatures, and once I get a feel for that, tone down the exaggeration to get more natural but still expressive expressions. I haven’t put in the time to test that suggestion yet.
Heh. That started as a scrap I was just going to throw out (circles I drew to practice expressions). When I got home and went to throw out my scraps I saw a character in it and I think I ended up doing more with that than any of the things I was planning to save that day and work more on.