Filed Form 1120 TYE 12/2017 which had a NOL.  return was filed by due date.

Did not elect to forego the carryback period.

Can an Amended Form 1120X still be filed for TYE 12/2015 to take advantage of the NOL from 2017?

If not, can Form 1120 TYE 12/2017 be amended to elect  the Forego of NOL carryback and carryforward the NOL from 2017?  

Ken A.