My passion is country music, and I can sing songs as low as no rush by josh turner or even as high as roll with it by easton corbin (just to give you an idea), so I have decent range, My only issue is, once I sing for a period of time, say 20 mins +, my voice starts to get raspy and I am no longer able to hit low notes, or even normal speaking tone. This hoarseness is not my voice getting strained from singing, rather I just lose my low range and cant talk normal I have heard this is because when I sing high I am using too much head voice, and when you try to go back low it doesnt work. I want to be able to keep singing high and go back low and talk without losing my voice whenever I want, and one of my goals is to play some local gigs. Any practice tips or advice is much appreciated, Btw I'm a 17 yr old male, thanks this problem rlly sucks!
Short answer: your technique is wrong. I dont know what, but you are obviously doing something wrong. You are straining your voice, so it gives out after a while, and when that happens, you loose some of your range, on the top, but on the bottom as well. Also, when you start to sing, your voice isnt warmed up, and that makes is lower. When it warms up, you get a bit higher. So its probably those two things that compound on each other.

The only thing that you can really do about this, is to get a teacher. Its almost impossible to correct such things without seeing and hearing how you sing in person. A good teacher will show you how to breathe, how to give correct support, shape the vowels, and how to use your lowest and highest range. You can try youtube videos and other stuff like that, but without having someone to correct you, its gonna be really hard. And if you continue what you are doing right now, you risk damaging your voice permanently.
Joža je kul. On ma sirove z dodatki pa hambije.