How to tell if baby is getting enough breast milk?

I'm starting to worry that I'm no longer producing enough breast milk for my baby. Now that she is eating solids it's really hard to know, then to top it off I recently found out I'm pregnant with number two so I'm worried about how that will impact my supply.

Any suggestions on how I could increase my production at this point? Or tips on how to know for sure she's getting enough milk?