You asked for it I don't get the sense that it has anatomical foundation. Until you get used to including that foundation work in your sculpts, try starting on graphic or tracing paper. Draw your character on one layer, then over that draw what it's skull and skeleton would look like. This will force you to think about structure, and you'll have to make adjustments to your original drawing to compensate for the skeleton. Then make a superficial muscle sheet over that. You don't have to spend a long time on these to get them looking beautiful, you just want to have something well thought out before you go to 3D.
Also, get some great anatomy refs and pin them up on the wall around where you work at home. Sometimes I'm too lazy to go fetch an anatomy book when I'm working, but nobody is too lazy to look up at the wall. It helps, trust me.