So I noticed that you tilt your head back and look up a lot whilst you sing. I realise this is because you are singing to the heavens, but doing this really increases the pressure on your vocal cords a lot. Looking down to the floor also does the same by crushing the voice box. It's a good idea to keep your head level when you sing. Try singing a long note and move your head up and down and see what that does to the sound you are making...you will hear a difference. You should find that keeping your head level enables you to sing for much longer periods without tiring your voice out.