The IRS is severely backlogged on mailed returns, to include amended. All you can really do is wait. You can check the status of an amended return at https://www.irs.gov/filing/wheres-my-amended-return
It takes at least 3 weeks (usually longer) for a mailed amended return to show up in the IRS system. But with the severe backlog they're dealing with now, it would not surprise me at all of your amended return is still not in their system even though you may have mailed it months ago.
