Er, what did you do exactly after trainer challenges? What deck did you use?
The usual route is to first buy one of the two latest theme decks for 500 tokens. They both are noticeably stronger than earlier decks. Then play versus in theme format. You'll need at least 50 games to learn how to play the deck optimally, but you'll win a decent percentage of those games since your deck is just as strong as your opponent's and you should be matched with an opponent of a similar level of skill most of the time, so you'll earn lots of tokens and stuff. (Actually 50 games is real quick, it's really difficult not to misplay even in theme decks, and playing optimally means buying and playing with the other decks too.)
Oh right, streaks of bad luck are normal. Bad draws for 5-10 games. Thankfully there's streaks of good luck too.
By the time this gets old you should have many more cards to help build your first standard deck.