My signal from the tower(s) fluctuates & Causes significant Buffering

I live in a ground floor apartment. I have my T-Mobile gateway located in the only place in my apartment where I can get 4/5 bars. As long as the gateway remains at 4/5 bars my 3 devices (2 fire TVs & laptop) have no problems. However my problem lies in the fact that 4/5 bars fluctuates daily from 4/5 down to 3/5 down to 2/5 and even completely loses the signal from time to time. My tvs buffer frequently and its become very aggravating. I've never achieved 5/5 bars and cannot seem to hold 4/5 bars consistently. And the fluctuation can occur any time of day or night. There doesn't seem to be any rhyme or reason. I cannot predict when it's going to happen. I'm am old timer that recently cut the cable cord but I'm afraid im in over my head trying to bring issues such as this to resolution; especially if there's going to be significant cost involved. When I used the mapper I noticed that I have 3 different towers relatively close to me. Which makes me think perhaps my signal is jumping from tower to tower??? I don't know. I could certainly use HELP understanding what's actually occurring and how to remedy without being forced to spend a bunch of money to do so. THANKING THE COMMUNITY IN ADVANCE FOR ASSISTANCE. Don S.