Not sure if this is the right place but I'll post here anyway

Been playing for a year and a half, joined a band on rhythm guitar and vocals, etc.

I've got some problems though:

- Some bar chords (A...) seem a bit painful still, even though I've been playing them for ages. I'm guessing wrong technique here or something.

- Know a few scales, can't totally remember them by name.

- I can play a few songs (Sunshine, Immigrant Song, Sultans of Swing) but can't really solo well. Then again, I don't like showing off.

- No confidence man.

So, yeah, bar chords are pissing me off. Don't laugh.
I'm not exactly sure what you are asking about. But I can say in a band and most things in life confidence is key. If you think you suck, then people pick up on that and also think you suck.
I'd say keep on practicing, bar chords can take some time. I've been playing almost 3 years and they still aren't always perfect all the time. Maybe play around with your hand positioning on your chords. I know when I play an A chord rooted on the low E string I have to turn my hand back to more a classical hold. If I'm playing a bar chord rooted on the A string I usually have a baseball bat grip. Everybody does stuff differently, with practice you'll find your best way of doing stuff.

If you are in a band it will really help to know the names of your chords and scales and have at least a basic understanding of key, harmonic majors and minors and how they work together.
I sometimes use my thumb over the neck from the top to cover the E + A strings if my hand gets sore from barring and don't worry about being able to shred, I find rhythm is my stronger point anyway and so mess with it instead. Music can be a bit crap without a decent rhythm after all.
You have 3 options, you either work on your weaknesses and make them strenghts or you ignore your weaknesses and work on your strenghts, 3rd you work on both.

Evaluate yourself, if your weaknesses cant be ignored then work on them.
Work, practice, practice and practice more.