My ex claimed our son on his taxes. I mailed in my return claiming my son, what should I expect?

I had e-filed and it was rejected because my ex got to his taxes first. I called the IRS and was told to mail it in and they would send out notices and investigate when they processed my return with the same ssn. What can I expect? Has anyone been through this? We were never married. We lived with him for 3 months... show more I had e-filed and it was rejected because my ex got to his taxes first. I called the IRS and was told to mail it in and they would send out notices and investigate when they processed my return with the same ssn. What can I expect? Has anyone been through this? We were never married. We lived with him for 3 months out of the entire last year. I supported our son on my own (I have copies of 2 checks he gave me for all of last year, totaling $350) he still saw him but it's been random. I do have a child support case opened on him but it's yet to see a courtroom. How will I prove support? Is it all on me to do so? I do know that his tax returns from years previous are questionable, if I have them take a look at those, will that be enough?
Update: There is no court ordered custody in place. My son is only 1 so there are no school records and I ended up having to quit my job in order to take care of him. I did have a babysitter for quite some time to watch him while I was at work. She is a family member though. Would it suffice if I provided an affidavit from... show more There is no court ordered custody in place. My son is only 1 so there are no school records and I ended up having to quit my job in order to take care of him. I did have a babysitter for quite some time to watch him while I was at work. She is a family member though. Would it suffice if I provided an affidavit from her?
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