Sheesh. Needs a bit of a balance pass through. The beginning of the game is difficult but got easier as time went on for me for the first playthrough. However, when I tried the green girl I could do zero damage, and eventually had 4 bosses on screen at one time including almost every single enemy type. Here's even a picture probably 100-200 seconds before I died because I found out space bar does a thing which kills you.
Edit: after playing for a bit I guess green's special does some kind of AOE attack and it helps a lot. A balance pass may not hurt. Also would be kind of cute that if some of the upgrades changed the PC, like each mega milk you get it would reflect in your breasts, or the speedy thigh-highs if it changed the color of your current ones. etc.. enjoyable game.