First of all - Good for you for not giving up. That's how we succeed. Just going forward. That's all it takes, and eventually we -will- get to where we want.
You don't necessarily need a trainer in order to be pushed and to exercise harder. Sounds like you're only doing cardio, but want to try other stuff? That's good
There are plenty of strength training posts and suggestions down in the Exercise section of the forum, and people much more knowledgeable about the subject will probably be able to point you in the right direction. There are stickies there about it, too.
Or find a sport/exercise you've always wanted to try and sign up! Doing different things for activity is good and healthy! =) Keep at it.