You can amend your 2014 tax return now if the amendment shows that you owe money. You cannot amend the return until you get the 1099-R.
It sounds like the amount that was in the 401(k) is fairly small. If the amended return shows that you owe only a minimal amount of tax, it's not necessary to file the amendment.
There is no reason to call the IRS. You should not call.
You can see if you owe any money to the IRS in Your Online Account on the IRS web site.
