IPhone 6 only able to connect to 5g networks?

Okay so I got my 6 (used) around Christmas time. 1-2 months in and there were no connection problems. Around 2 weeks ago the signal began to dropoff from my family room, and slowly began to deteriorate as days went by. Now I can't connect to my main Wi-Fi network unless I'm like a foot away. I solved the problem by simply connecting to the 5g network, however the same problem applies anywhere else. I can't connect to any of my friends Wi-Fi since it is not 5g, and I was wondering if there's any solution to this.

That's 5GHz not 5G, that's something totally different and your iPhone 6 can't connect to 5G mobile networks.

So your iPhone won't connect to 2.4GHz networks unless you are really close. It sounds as though the internal antennas are either damaged (from dropping or similar) or a part of one of the internal chips is failing. To be honest, the fact that the connections are gradually getting worse actually sounds like component failure. You can try to get the phone fixed, but this is probably going to cost as much as the phone is worth - welcome to the wonderful world of Apple!

You are confused about the connections, 5g not available yet…3g and 4g which are your phone network supplier, seems your Wi-Fi signal has dropped, comment with iphone 6, toggle the airplane mode on and off which will restart the Wi-Fi connection, if drops continually, power off iphone, open pc/ itunes, connect sync lead to pc, holding the home button in, connect the sync lead to iphone, recovery mode now, re-install