Ouch! many things going on here. umm first thing is playing live is soooo much different to playing at home at low volume or through headphones, much practice with the band is required i suspect. You will get used to it and also finding a sound you can hear through the rest of the band as again the settings you have at home don't always work in a bigger room could be many reasons ie: what the floor is made from, how high/low the ceiling is, are you elevated above the crowd etc
It is hard to hear what you are playing if the cab is low down by your knees but getting tight with the other members especially the drummer will help to cure that, if you play anywhere that provide monitors get them to cut everything from yours apart from bass may help as it will be infront aiming toward your ears.
Hope this helps a bit, im sure you'll be given many many other hints a tips from the more experienced boys on here.