Thief @ 80
First off, your gear doesn’t matter in sPvP.
Did you set-up your PvP build before joining a game? If not, go into the mists and click the “PvP build” button on the top. Then make sure you select the Berserker amulet. You can also try various different rune-sets, all with different strengths. Runes of Strength are a popular choice for all classes at the moment.
Sigils can also be picked for weapons. If you’re looking for burst, Sigil of Air is a good choice but there are a number of viable choice. Try them out and find out for yourself.
Anyway, I assume that’s the problem you’re experiencing and that it doesn’t have anything to do with your play-style.