Whoah, this is an old one, Sunray, so not sure if you are still trying to get someone's thoughts on this.
I can only give you my personal point of view.
I do not think that I would act as if nothing was wrong when my husband would not write to me while being in prison, especially for seven weeks!
And at the time you posted this, you were counting three weeks again.
I believe if you explain to your husband how you feel when he does not write you, that maybe you'll get worried or just plain crazy without hearing from him, it will make the situation more clear to him and he may realize that he can not just give in to his feelings. That there is still someone out there who cares and loves him. Someone for whom he has to keep trying and work through these feelings.
Your husband may not have exciting things to write to you ( and I don't mean to be disrespectful or so....just understating) but he should know you are there, waiting for him, for his letters.
Because you love him and want to know how he is.
Even though he may not feel like writing you a book but just a few lines or one page would make all the difference, if it was only to reassure you that he is okay. In my opinion he has an obligation to do so. You are his wife.
If you do not tell him how you feel, and he doesn't seem to sense what having no mail for such a long period of time does to you, then nothing will change.
Maybe these periods in which he thinks of what he has done to get to prison, should be the periods in which he really
should write to you.
In the end, it is what it is.
Maybe by trying to work through his feelings, little bit by little bit, will help him to deal with it better and will bring the two of you closer.
I think that being honest about how you feel is the best approach.
He is not alone, you are there for him but he should be there for you as well.
Good luck!