I'm using betterment and I contributed $5500 to a 2015 Traditional IRA. This is the first time I opened an IRA. If I convert this 2015 contribution to a Roth IRA right now (because I can't contribute directly), how would I make a contribution to that Roth IRA for 2016?

I'm confused about how this works...  
1) Would I only ever be able to convert once from a traditional IRA to a Roth IRA and then never be able to contribute to that roth ira again?
  
OR
  
2) Would I open up a new traditional IRA for my 2016 contribution and convert that into a separate Roth IRA, so now I would have two Roth IRAs??   

OR
  
3) Would I open up a new traditional IRA for my 2016 contribution and convert that directly back into the original RothIRA so I would only have one Roth IRA??  

OR  

4) Would in the first case, I rollover the 2016 roth ira into the 2015 roth ira right away?

Any clarification would be great if you can help me clarify how I do this year after year if I want to contribute to the roth using the backdoor roth ira strategy?