This whole song is basically just the same chord progression repeated over and over again.

***

Ebm            B

I just had sex

            F#        C#

And it felt so good

***

Then you take it up a half-step for the key change at the very end.

Em            C

I just had sex

            G        D

And it felt so good

***

If you'd prefer to play the whole song with a capo on the first fret, try this:  

Capo I

Dm            Bb

I just had sex

            F        C

And it felt so good

***

Then the key change at the end with a capo on the first fret would be:

Capo I

Ebm            B

I just had sex

            F#        C#

And it felt so good