Read it a year ago forgot the name but i think it's about a boy band and the main is just a newly added member to the group and he's got an unique voice but still needs a lot of training to polish his voice or something like that but some of the members don't like an amateur joining or something like that. I forgot whether it's yaoi or shounen-ai or maybe neither of them.

that's all i remember but anyways please just throw any names of mangas that's about boy music bands professionals not indies.

think your talking about this one:
Given

Shounen Note was the first to strike me but I'm damn sure that's not the one because it was a school choir and definitely not a band. But it's a fluffy story nonetheless. 🙂

nope none of those, it's actually eye catching with pretty boys though

These don't really match your description, but they're ones that came to mind when you say bands and pretty boys.

Presentiment
Gravitation

Seifuku no Tame no Love Song is about a band but I don't know if it's what you're looking for as I haven't read it yet.

Is it 'Gomen Ne Idol-kun'? 🙂

It may be this one called "Yoru to Asa no Uta".

Might be Teen Spirit, though on the off chance that it is this, be warned that this has been discontinued due to the author's death. 🙁