I've been taking singing lessons for a few months now and one notable thing is gaining confidence with my head voice. Previously I probably never used it, now as well as my chest voice being able to go much higher (A2 - E4/F4) I can confidently sing some fairly powerful head voice notes in the range D4 - Bb4, and can reach B4, in a relaxed manner that doesn't strain my voice and feels quite natural.
However above B4 I notice I have to switch to a much more forced technique, and have far less control. I sort of have to "throw" my voice and hope it hits the right note. I've tested with a vocal app and I can reach C5-E5, sometimes as high as G5, and hold the notes in pitch, but it's really just a squeak not something useful. And it tires my throat out very quickly. And I feel stupid doing it which is a big factor for me personally.
I believe this is me switching from head voice to falsetto and wondered if there are specific techniques and exercises I can use to develop this part of my range... and if I should be using this technique or instead trying to expand my natural voice higher rather than trying to sing these very high notes at all in this style.