I have 2.5 bath home and we recently had a cold front come through (not sure if that matters) but all 3 toilets have started backing up not overflowing just not flushing correct. Im also hearing sounds from the pipes in the bathrooms kind of like bubbling sounds. My showers and sinks all seem to be draining fine. Oh we added the second full bath about 4 months ago.

Hmmmm.. sounds like it could be a clogged vent stack... maybe a nest or bird or leaves in the stack... would need to go to roof and look down the vent pipe to determine if there is a clog in the pipe.

BUT...the new bathroom makes me curious...did you guys hire a professional to install the bathroom? Did he hire a licensed plumber..? Were permits pulled..?
Is the new bathroom directly above the old bathroom? Did the contractor run a separate waste stack up to the new bathroom or did he tie into the existing waste stack? Answer these questions as best you can and let us know and we will try to help more.