Hi Shavell,
I'm starting with the assumption that you did your own battery and screen replacement, so let me know if that's incorrect.
As well, I'm guessing you weren't seeing that behavior before the replacements, so the logical conclusion is that the problem is related to your repair somehow. The most common issue we see in cases like this are the flex cables not being fully or correctly plugged, although occasionally we see that a cable or connector was damaged during the repair.
So the first step here is to retrace the steps of your repairs and unplug, check, clean and reseat all of the the connectors you unplugged during the repair. That's going to include the battery, digitizer, LCD and home button connectors. Examine each one with a magnifying glass and a bright light for bent or broken pins or dirt or foreign objects interfering with the connection. Bent pins can frequently be straightened with fine tip tweezers if any are found. While you're at it, check the flex cable going to each connection for any signs of damage; tears, gouges or nicks in them.
Next, you'll want to take some 90% or higher isopropyl alcohol and clean both sides of the connectors; the one on the logic board and the one on the cable. Plug the cables back in carefully, paying special attention to the notes on steps 17 and 18 of the iPhone 6 Battery Replacement guide regarding the display cable popping off and the proper way to reconnect those long plugs.
Once you've got everything reconnected and the covers back over the plugs, retest the phone before securing the screen down and see if the problem has been fixed.
If not, you may have an issue with the replacement battery or screen. Try putting the old ones back in one at a time and see if the problem is still there.
After you've done all this, get back to us here and let us know what you find. If the problem still hasn't been resolved, we'll figure out what to do next to help you.