I know of some artists that create a reference page for their characters. It's great to establish your style and your character's distinctive features in a way that is easy for you to refer back to when you become uncertain.
As for how I've kept and developed mine, that came through trial and error as well as watching other artists. I learned from those wiser than me and it helped my style develop at a much faster pace.
One last thing, try not to confuse "inconsistent style" with natural development. Judging from your first picture to your third, it looks more like you've improved a ton in just those three slides! That's amazing! Your character looks much more lively in the last picture than the first.
I hope you don't mind, but I used an example from my own comic.
On the page below, it doesn't look too terrible, however the color is lackluster, the chat bubbles aren't clean, and the dialogue could have been written better.
This is a similar page drawn a month later. The color is much more vibrant, the city actually looks like a city, and the chat bubbles are clean and legible.
At the end of the day, it's your comic and ultimately, it'll be up to what YOU want to do with it. You're improvement is evident in just the little you've shown us. I don't doubt that you'll find what works for you in no time 