toilet slow to evacuate and slow to fill up after plumbing work done

Hellol!
This is my first post in the forums.
I've been having trouble with my tub draining for a while now. So, I had a plumber out and he replaced the cast iron pipe and trap that was connected to the larger pipe going to the sewer. He tied in plastic piping and a plastic trap. Now, the tub drains better than it ever has, but when I flush the toilet the force of flush is so weak that it's almost as if it's not flushing. The toilet bowl takes a while to fill back up as well. What could be causing this?

Thanks in advance!

I have no Idea without more information or, being there to test it myself...
Clooged toilet?
Clogged line?
Toilet in need of repair?

Take your pick!