It is not uncommon for adult children to go through periods of not communicating with their parents. I understand your hurt - sometimes I don't hear from my daughter for what seems like months on end.
I would suggest that you resist the urge to tell your son about your suspicions. This will only cause major damage to your relationship with your son and your daughter-in-law. I think it might prove very embarrassing once your grandchild is born! Try to make a good relationship with your daughter-in-law - she is the ticket to any future grandchildren. A good relationship with your daughter-in-law is just healthier for all involved. Why waste valuable time being suspicious? Keep the lines of communication open and try to see that your daughter-in-law wants your approval. Why else would she send you the ultra-sound picture?

Laurie
In the meantime, I think you can find great happiness if you continue doing those things that give you great pleasure - going out with friends, perhaps exercising, or finding a new hobby that you really enjoy. Life can be really great when we are no longer burdened caring for children!