My iPhone 6S can never find Wi-Fi?

For example, when I'm in my bedroom, my macbook will have full Wi-Fi bars, my girlfriend's iPhone 6S plus will have full Wi-Fi bars, but mine will have only one, and eventually disconnects altogether after a couple minutes. I've tried taking the case off and re-booting the phone - doesn't help. I've also tried making my phone "forget" all Wi-Fi networks, then reconnecting. And yes, my phone is connected to the same network as the other devices. Thank you!

Added (1). Also - my GPS locater has a very hard time finding where I'm if I'm not connected to Wi-Fi. I have AT&T, and so does my mom. When we're standing next to each other, her iPhone 5 knows exactly where we're, while mine hardly knows what town we're in (giant blue range circle).

Call Apple Support - generally, you would try restarting, resetting, then reinstalling; however, the Wi-Fi function is built right into the operating system, so the only way to uninstall/reinstall it would be to reinstall the operating system.

Did you try "resetting" the network? Here is a statement from iPhoneHacks "Most networking related issues I've experienced have been fixed after resetting network settings. Resetting these settings flushes caches and clears DHCP settings and other networking related info. To reset network settings, open the Settings app and navigate to Settings > General > Reset and tap on Reset Network Settings." The article even has pictures for you.Http://www.iphonehacks.com/2016/09/fix-ios-10-wifi-problems.html
It is worth a read, there are other steps listed.
As another resort, visit an Apple Store or contact Apple support. There are lots of people with these issues. In some cases, I think the internal Wi-Fi antenna has come loose. (Just a guess but year of other devices make that very possible.)