My weights are WAY too light for me. What can I do?

Hi guys! This is basically as the title says. I'm 15 years old, and I've been regularly working out with FB for a couple months now. I'm generally very healthy, but I have some belly fat I want to cut down on, and I am hoping for a more toned stomach as well.

Anyway, the dumbbells I am using are 1 KG, which is super light. I hardly sweat at all when I go through strength training workouts, and I feel bored rather than tired.

What weight would you guys recommend, and where can I get them at a cheap price? (My Asian parents don't give allowance, and I haven't started working yet, so I'll have to ask them for money)

Thanks :)