I'm a 14 year old boy and I'm pretty sure my voice fully mature like a year ago but I recently, as in a week ago, lost a few of the higher notes in my falsetto. I am wondering what I what I can do to get them. I am also wondering if it might have anything to do with me extending my chest voice and head voice

Hi, Jack! Your voice will continue to change and grow throughout high school and even into college. While your voice is in a stage of transition, we don't want to force higher pitches than are currently comfortable.

That said, the safest and gentlest way to exercise your falsetto range is to sing through a straw or another semi-closed position (like MM, NN or NG). I also like the HW shape described in this lesson. 

thanks 

You're welcome!