Forex Losses from 2015.

So, I had some big losses in 2015 and 2016. I never elected to be treated under section 1256; hence, I am treated as a section 988 trader. This means that my income (and loss) is supposedly treated as ordinary on line 21 of form 1040 (2015). I have never filed my 2015-2018 tax returns (as I am an expat), so I do not think the 3-year limit of the statute of limitations would affect me for recognizing and carrying over losses. However, I am unsure if I am eligible to carry over losses from 2015/2016 if I traded Forex/CFDs which are both section 988 (according to hours of research that I did). I only find answers here that say that an unlimited amount of losses can be deducted for the year. But, I am unsure that this applies to other years, and if so, how would I even do this? What form would I use?

Thank you.

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