If your son e-filed and did not say he could be claimed, but now has amended, that's fine. But you will not be able to e-file your 2018 return this year. It will have to be printed signed and mailed. It takes 3-4 months for an amended return to be processed. His SSN is in the system as having been used this year, so you cannot e-file your return that claims him.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**