I know just how this feels - internalizing everything and not being able to cry. Although I can not help you with why this is the case for you, I can tell you how this came to be for me.

For me there where many reasons as to why I wouldn't allow myself to ( Years of physical - sexual - mental abuse) and then couldn't anymore. This all changed for me after the death of my daughter. At first I refused to cry then after 4 years I could no longer hold back the pain. Since then I have not stopped crying. Yes it took the death of my child to learn how to cry again. And although some may think it is weak I no longer care.

Perhaps because you have gone through so much is the reason you are finding it hard to let go and cry. Don't be hard on yourself this can be a defense - survival mechanism our heart uses to protect use from too much all at once.

I'm sorry I do not know the answer. But I can be here to listen with everyone else.

I hope this comes across the way I have intended it to.