Volume problems

What sort of amp are you using? Is anything running through a PA system? If it is a smaller size amp sitting on the floor you could raise it up closer to head height in your direction or lean it back so it is more directed to your ears.
Another issue could be were other the people are standing and the direction of their amps.
Hard to say without knowing the type of amps the band are using and the layout.
You could also trying having more/less beer.

It really depends. Maybe you weren’t infront of your amp, maybe everyone else was too loud and you didn’t hear yourself, maybe it was the room you were playing in. If you used a mix console maybe the sound guy messed something up. It’s hard to tell why you didn’t hear yourself.