RAM for my motherboard

So I was trying to play Mass Effect: Andromeda and quickly realized I needed more RAM. Now the problem is that my motherboard the ASUS Sabertooth 990FX r2.0 for AM3+ chipset has a very limited series of ram to choose from. However when looking up the RAM, I have one working stick of the corsair dominator 1866 MHz, none of it seems available anymore. So does anyone here know if I can just upgrade the memory kind of randomly or am I just kinda screwed?