I made a backdoor Roth conversion ($5500 IRA contribution followed by conversion) in March of 2018. How do I account for this on my 2017 return (I have no 1099R yet)?

Basically I want the conversion to be accounted for my in 2017 return (I was planning to make another contribution to my IRA followed by a conversion in after April 15th 2018 to get back on the same annual cycle).  Since the contribution and conversion were made after December 31st (but before April 15th), I thought I could file them with my 2017 return.  I could not however obtain a 1099 R for the conversion from Schwab because they told me they are released at the end of the calendar year.