My bike's chain vibrates with every pedal stroke
It's important to remember that while your mom would kill you if the bike breaks, she would be so much more upset if you did get hurt! Moms are weird like that, so don't be afraid to ask her for help with the bike, or money if something important needs fixing.

So how to fix the bike, we need to figure out why the vibration is happening, so that means inspecting the bike as best as possible. 

You mentioned the pedals, so we can start there. Are both pedals fixed to the cranks securely? Do the pedals feel nice and smooth to turn, or are they rough and noisy?

Can you wobble the cranks side to side, or are they nice and stable? They'll spin forwards and backwards, but you should't be able to wiggle them side to side.

The chain runs front to back, is there anywhere along the chain where it rubs on something that it looks like it shouldn't? does the vibration depend on which gear you're in?

Check the rear wheel, when you spin it forwards, does the rim, or the tyre wobble side to side? Does the tyre touch the frame of the bike at all anywhere? It shouldn't. Make sure that where the wheels are held in the bike, they haven't slipped just a little bit out of where they should be, and that the brakes look like they aren't interfering with the wheel turning.

I shouldn't really answer the question with lots of questions, 'site rules', but the goal is to help you have a good look over the bike, then you can update the question with some of the findings, and anything you think is out of the ordinary. Maybe some photographs of the bike where you think there could be a problem.

There's a system of inspecting the bike known as an M-check, see a page here, which might help you look for issues, but I'm not sure that it would help you figure out this particular vibration or not. It's a good check to learn about though.

If you don't find much with these suggestions, or other people's, then its a good idea to have the bike looked over by someone who knows about bikes, maybe a bike shop mechanic or a family friend. If you've noticed this problem, and it's getting worse as you ride the bike, then I think it is something worth getting fixed.