I've had similar problems, depending upon where I am in the house.
Tried a WiFi signal booster but it didn't work. I have a friend who is an IT specialist, and he said to get the kind you plug into the wall and it uses the building's copper wiring to boost the signal. Looked at 'em on Amazon, but for now I'm sitting on the ground floor closer to the router, or up on the third floor where our bedroom is I will often use a neighbor's open network.
Good luck.