Ok, im new to vocals, and need some coaching!

I just recorded myself and figured that i sing a little flat... so i raised it, and as i can tell, its a little better in parts...

One problem:

I hit the lows of the song flawlessly as much as i can tell, but when i start getting higher, by voice tightens and it seems like my nasal passageways tighten... (This is just what i feel like is happening im not sure)

It feels like the air is hard to push out at that higher note(s)

Maybe someone can tell me if im not using my diaphram correctly, or just dont have the ability (yet) to hit that high of a note?
Guitarist in learning...

Guitar :
Ibanez RG220b 24 fret, blocked floyd

Palomino 30watt tube amp, 1x12

Old Equipment:
Line 6 Spider II 150 Watt ( 2 12s ) (SOLD)
Mesa Boogie Dual Rectifier 100 watt, 4x12 (REPLACED)