Singing in key without music

Hi guys... Im a singer and bass player in a cover band. I have a problem knowing what key to sing in if i dont hear the music. If i sing without music i can guarantee it wont be in the right key, allthough whatever key i start in will stay in tune. When singing songs that start with vocals i have to strum the first note so i know what key to sing in... N now we are playing at bigger venues and the amps are so much louder i sometimes even struggle to hear what key the guitar is in and have noticed sometimes when the lead guitar comes in that i am flat. Im fine if im doing harmonies and can go off the lead vocalists voice and once i can hear the key the guitar is in im fine. Has anyone else come across this problem? What is it called and how can i fix it? Any help would be grately appreciated. Cheers, Ste

It isn't easy to sing a specified note out of the blue with no reference pitch.  Are you saying that you have a song that starts with you singing without instrumental accompaniment, and then the rest of the band comes in?  Don't beat yourself up over it, don't risk being off, there's nothing wrong with giving yourself a note.

Not quite sure I understand the problem you are describing with respect to the larger amps.  Is it so loud that you can't hear yourself?  

I can hear myself, but sometimes when the drums are being belted and the guitars are goin for it n ringin out from the stage its like i hear 2 keys n when i listen back im sometimes a bit flat, i only realise when the lead guitar comes in or backing vocals n then i adjust. The other singer in the band can sing in key without music but on the other hand if we transposed the song he would still sing in the original key and be out! ... Yes songs such as the script - for the first time or david gray - the one i love. I have spoke to a few singers n they dont have the problem with the guitars either. Im fine when we do acoustic gigs. Wierd but id feel so much better if i could get to the bottom of it