Singing is a form of physical skill where you are using muscles that run from your diaphragm, your lungs, rib cage, throat, vocal apparatus, tongue, lips, and nasal cavity. Like any other physical activity there are many ways to do it and some ways could cause damage if you try to push your voice harder without understanding some of the mechanics. Muscles do matter, but its not the kind of "six-pack" musculature we associate with being "fit". This is why some peeps with great voices can be distinctly porky!

I agree that some good coaching could be what you need; it is not possible to give you helpful advice without having seen and heard you sing, because there can be any number of factors affecting vocal production. Whilst some teachers may have a narrow focus (e.g. Stage musical style) there are teachers who are knowledgeable about many styles and are interested in helping you to develop your unique voice.
999 has made a good offer; you could start with that. Good luck and enjoy the journey!!