Actually, it is being ascertained that even in RRMS, the same as in SPMS, there is "progression", albeit more silent and less noticeable, in between relapses, so those types of "classifications" of MS (i.e. RRMS, SPMS, PPMS, etc.) are fast becoming outmoded. They are still used, but it's becoming almost impossible to determine the difference between RRMS and SPMS since the determining factor that differs between the two is becoming more and more blurred and increasingly difficult to determine. It boils down to "rate of decline".
IF you believe that "permanent" disability is happening more rapidly in between actual relapses and exacerbations, it is most often then referred to as SPMS. But again, telling the difference between the two is becoming harder and harder for even the educated professionals to do. That's probably why your doctor asked YOU what you thought you had.
True "primary progressive MS" is a little easier to determine, because the two main criteria is the rapid decline to disability without experiencing "remissions" of any type, and from the lack of inflammation in PPMS that is evidenced in RRMS and SPMS.
There is a push now within the MS research field to get rid of those types of classifications altogether and change over to "patterns" of MS instead. Which more aptly defines the different pathogenesis that is taking place in various forms of MS and basically has nothing to do with "rate of decline" or "relapses". That would also make tailoring drug treatment for different patterns of MS easier to accomplish. Not everybody has the same biological or pathological activity which leads to their exhibition of or diagnosis of MS.
Hard to explain, which also paradoxically HELPS to explain why it is so difficult to determine between RRMS and SPMS. Only true PPMS sets itself aside clearly from the others.