When you play its great.
When you sing though.
Its no good using just the tops of your lungs and forcing it, the result is squeaky. What you need to do is go right down and sing from your stomach, use that area for breathing while singing. Keep your chin up and level too, plenty of people who play and sing drop theirs to look at the guitar and cut off their voice in the process.
Forgot to add... serious is almost right there.
When I used to sing in choir and on stage our bloke who taught us the songs and parts used to have 3 kinds of people, pear, apple, and pigeons.
Majority of people used to be pigeons.. theyd breathe using only the top part of their lungs, which is fine for day to day stuff, but hed tell them to practice breathing properly.
Pears... people who were conscious of people seeing them singing... theyd breathe great.. fill their lungs, but then tighten their chests when nervous and dampen their voices so others sung over them and they couldnt be heard as much.
Apples... people who had gotten over the pigeon and pear stages... learnt to breathe using the whole of their lungs. its the shape their chests will make. Notice operatic singers have full chests, and stomachs when singing.
Everyone is a pigeon or a pear... you just have to relax.. breathe... and sing. Dont strain or hold your breath... if you need to breathe in a song, breathe. Like I said, do a dry run, find out where your weak points are... sort them out, then sing properly
If you want to sound good, you dont need fancy equipment just put some effort into your singing, if your sounding crap try again and again for like an hour or so until youve nailed at least one section of it. I used to have to do it for rehearsals (singing "I can show you the world" from aladdin to myself in the study was a rather embarassing experience when my mates came to call one day
lol but it was a thing I had to do) just give it a go