Please take a read through the "unhealthy fish" sticky and provide as much detail as possible.
I will say your water parameters are essentially impossible. Nitrate is the end product of the nitrogen cycle. In a cycled tank you should see nitrate, in an uncycled tank ammonia and/ or nitrite should be present depending on how far progressed your cycle is. Seeing nothing is a bit of a red flag to me, and could mean you have a water quality issue you arent aware of.
The only way to realistically get zero across the board like that is if you did your water test immediately after a near 100% water change and all you are effectively testing is tap water.
What test kit are you using? Make double sure you are testing correctly. If you still see zero everywhere get a 2nd opinion.
Im not an oscar keeper myself but my understanding is they are very fussy about water quality. They need pristine water and a very clean substrate (or bare bottom) and a water change every 2 weeks doesnt really provide that.