My son was hit by a truck and hurt very bad, my ex has retained a lawyer, Am i able to sue due to the Mental Anguish and stress this has caused me?

Probably not - assuming you were not in the accident and assuming it occurred in North Carolina, you won't have a claim.  I am sorry to hear about your son, but hopefully your ex husband has hired a good, qualified attorney who will maximize his recovery.  Good luck going forward.