Hi. your plant looks healthy. But it is definitely small. What are you using for soil? It looks a little on the chunky side. It might not be ideal for your roots to thrive in, hence the small plant. Each leaf set should be bigger than the set before it. Yours are all same size (small). That is a sign of stunted growth. Not a big deal really, no need to freak out. Its in a pretty big pot. It might just be busy making a strong root foundation and the above ground part will eventually catch up.
Ditch the tinfoil. It reflects more heat than light. It reflects light your eye can see but not light the plant can use.
As far as fetilizer goes...if you must you can go to walmart and get some miracle grow N-P-K 24-8-16.
https://www.rollitup.org/view.php?pg=faq&cmd=article&id=106
Its the most common fert you will find. And will work well for you, if you mix it 1/4 strength at first. use every other watering. And work your way up to half strength.
OR
You can try some organic fertilizer. You can buy some online or from a garden center. You can make your own from molasses, compost, or worm castings. There are many many ways to go about feeding your plant. And it needs different nutrients at different stages of growth. try to learn about some of your options before you "just pick one"
https://www.rollitup.org/view.php?pg=faq&cmd=article&id=102
I hope that helps ya some. Everything you need for a successful harvest is here at RIU. Happy growing and good luck!