First off, I would say there are some stocking issues that need to be addressed. The pleco will get way too big for the tank. Also, the tetras would do much better if kept in larger schools... 6 or more is usually good.
As far as the tank not being cycled yet... I am surprised that at the 7 week point there is still a problem... and no nitrite. This means your cycle is stalled. What kind of tank maintenance besides PWCs are you doing? Are you cleaning out the filter and if so, how are you doing that? Are you using a dechlorinator product like prime to treat the water during pwcs? Have you put any medications or other chemicals in the tank during the 7 weeks?
You want to keep your ammonia at less than 0.25 ppm. If this means you have to do daily 50% water changes, then that is the best course of action.
I would also be curious to see test results on your tap water straight out of the tap. Especially for ammonia.
What makes you think your tank needs help? What problems (besides the ammonia) are you seeing? (fish behavior, water clarity, algae, etc, etc)