I have done the RC where you hold your nose and try to breathe through your fingers quite a lot. It usually feels like it is hurting my lungs. I did it a lot just to make sure that I wasn’t dreaming and my forehead ended up feeling like someone was twisting it. Should I not do that reality check?
Since it is giving you problems, it would be wise to stop using it for now or at least reduce the amount you are doing it.
There are many other RCs you can use. I personally love the finger through the palm one. 
sounds scary…
there are many other RC 's to do like reading text, count fingers, try to push trough a solid object etc. if you still want to do the pinching nose RC i schould just do it a little bit less harder, like just hold it a little bit
I have also been using this RC and have felt the pain of reality. This forceful inhalation won’t usually be harmful, but if you do it too regularly (ie. more than once a minute) you can do some damage and give yourself a headache.
(INSERT long boring scientific explanation of how the body’s internal negative and regular feedback systems work in unison with the equilibrium system that regulates blood acidity to give you a headache when the air pressure in your lungs decreases HERE >>>)
When you are dreaming, it won’t take any extra effort to inhale, so irl you should stop trying as soon as you feel you can’t breath. Or,if you find you need to inhale very hard to convince yourself you are awake (like me) you can try a RC that I call a reality equalisation.
If you have ever been SCUBA diving you will know that to equalise the pressure on each side of your ear drums you have to hold your nose and blow out. This is prevent the increased water pressure from collapsing your ear drums.
If you do this irl when you’re not underwater, you will hear a small squeak. If you do it in a dream you will be able to fully exhale or you will hear a continuous squeak as you exhale out you ears.