Why is my iPhone GPS acting wonky?

Whenever I'm driving and I turn on my GPS, it starts out just fine. However, as I continue on the path, sometimes the compass begins to float off course even though I'm going the correct way. Then Siri will tell me to "proceed to the route", even though I'm already on the route. Furthermore, if I do end up going the wrong way or passing up a turn, my GPS takes FOREVER to redirect me in the right direction.

I'm wondering if it is something wrong with the actual phone (I bought this phone used) or if the problem is with my service provider (I use Virgin Mobile which is owned by Sprint). If the second option is the issue, then I guess switching service providers would help?

I recently just started driving with Lyft, so fixing this problem is a must.

It sounds like you are using a navigation program that relies on mobile data.
That is a really bad idea… Mobile data connections are often very poor or erratic from a moving vehicle.

Get a navigation app that stores all data on the phone, so it's not reliant on outside connections to work.
I use the "Tomtom" navigation one, that is really good & work very well.

There are various others including some free ones.

I've been using Apple Maps. And Lyft uses their own navigation system that is ran through Google Maps. Even though people rave about Google Maps, neither of those work. I've also tried using Waze in the past, and it has the same issues.