So whenever I practice my voice, without my band. My voice feels great. I have resonance, and my head-voice is strong. A little tension in the throat (But I'm working on it I swear.) But when I practice with my band, it's like I lose everything. Almost no head voice, my resonance is shot, and I feel my throat tense up. So I really don’t know what's going on. Maybe I feel like I have to compete with the music, I don't know. But I'm wondering if anyone else has had this problem, and any suggestions?
Thanks.

Yep, you are competing with the band. vocal practice consists of a lot of open vowelsand not hitting the songs so hard. Band practice is tons of consonants and trying to hear yourself. Make sure you warm up properly before band practice and cool down afterwards. If you cannot hear yourself, try the suggestions in the book; get a good monitor system or if that;s not possible, try cupping your hand around your ear or better yet, invest in a VAM:)

I have the same situation. It's even worse now that I'm fighting a cold. I sat in with a band during open mic last night and the monitors were almost non-existant. After three songs I felt like I do after a whole night of singing. I think I may also accidentally fall back into bad habits and sing the songs the way I learned them (incorrectly) prior to taking some professional voice instruction. I know that quite often I don't get a full proper warm-up when it's just rehearsal at my buddy's house. I've been trying hard to reverse that situation.

Stress can also be taken into account. Singing when nobody is listening is not the same as when people are around even if they're good friends. You really have to get in your space to concentrate and not worry about how you sound and what people might think of you, etc...

Do whatever you can to turn the band down and turn yourself up. It makes it so much easier.