You have to report the carryover every year until it's used up. You can't skip a year. Even if you don't report it on your return you have to reduce it by the 3,000 (1,500 MFS) when you carry it over to next year. You can't choose when to use it.
This is from the IRS Pub 550 page 66
"When you figure the amount of any capital loss carryover to the next year, you must take the current year's allowable deduction into account, whether or not you claimed it and whether or not you filed a return for the current year. "
Here is pub 550… http://www.irs.gov/pub/irs-pdf/p550.pdf
BUT.....
If you have a negative AGI or negative taxable income it will show up on 1040 but it won't reduce the carryover to the next year. So you might need to prepare a 2018 return to see how much to carryover in case it is reduced.