It's good that you learn by hearing, but it will be better if you take lessons. It will make you a better bass play. 
Yep, but like MikeGee said, you have to find a good one.
But if you can't find a teacher, I think that if you 'structure' your practice time you can progress fast.
I use to just site down, play a few scales, listen to a few songs an dplay with them and call that practice. :| I wasn't really getting anyhere.
But now, I ssit down and follow a rountine like DJ's (posted here somewhere) and now I'm progressing much faster.