I'm practicing... and getting worse!

Hello all!

Last year, I became the lead singer in my band (as well as the bass player), so I'm really, really new at this, but I'm close to 40 years old. We had a garage gig in October of last year and I was weak, as you might expect. I started working on technique, but I don't have money for a coach, and don't have time to myself to watch YouTube videos. I do have a lot of time in the car, and I know that isn't the best, because I'm not in a good standing position. However, I did try (and you are going to laugh and laugh!) the audio 2 CD set from interlibrary loan of "Vocal Power", which sounds like it was recorded in the late 70s or early 80s (and it was- I remember because I had the cassette(s) back then). They seem to focus a lot on trying to break from the "breath-y" technique, but singing like that makes me sound a lot more nasal-y (and I apologize for the lack of proper terms here). My voice sounds a lot better and my tone is more even when I use a more "breath-y" (like the "hhhhha" type of breath, not breathing- of course I breathe!) singing voice.

I have some idea of my range, by ear at least, and it is not too shabby. I'm just really not that great. But here is the thing, since I've been trying to sing our band's new original songs over and over in the car each day- I'm getting worse! Not only am I doing things melodically and stylistically that don't work (I guess because I'm bored singing the same thing over and over), but I can't hold a note like I used to- at least it seems that way. I feel my throat tightening- I think my throat muscles are getting stronger, but this is affecting me in a not-so-good way. But the other thing is that I've lost weight- like 20 lbs from when I started.

I know that I need to find some way of practicing technique vs. just singing our songs, but the vocal power stuff was hard to listen to. So, some questions:

* Could losing 20 lbs. have negatively affected my voice?
* Was practicing our songs vs. technique what made me worse?
* Could a few hours a day of practicing five days a week build my throat muscles up so much that it could negatively affect my voice if I'm practicing incorrectly? (the "tight-throat thing")- I seriously doubt this, because I sang that much before in the car, but perhaps singing the same songs over and over and getting bored and singing in different styles, etc. has messed me up?
* Are there any YouTube videos I could convert to mp3 and burn to CD to listen to in the car for vocal technique (or similar audio CD solution) that you would suggest?

Off topic, but I've also noticed when I have a coke in the morning that stomach gas will inevitably screw me up at least once. Not that I'm in any position to give advice, but I think soda is an awful thing to drink before a performance.

One more thing- we have a gig coming up in days. Other than wondering "what went wrong", I could really use advice on what to do right between now and then.

Thanks so much!