Q: Bypassed my heater core and refilled my reservoir tank for coolant checked it after two days it's getting low again

I can’t help but think that there is a little more back-story here. But I presume you bypassed the heater core because you had a leak inside the car. That’s something you can do if you don’t need heat of course, though it sounds like that may not be the only leak in the system. The only way to see for sure is to do a pressure test on the system. There could be a small leak that is evaporating as it leaks so you don’t see a spot under the car. A pressure test should show that for you. In really difficult cases there is a dye that you can put in the cooling system that glows under ultra-violet light. Then it’s an easy matter to see the leak using a UV source. In any case, you can contact YourMechanic to have that checked at your convenience. They can send a technician to your home or office to check out your coolant leak and let you know what it will take to solve it.