Why is my data not working?

[AC Question]

I upgraded my s4 to Lollipop (5.0.1) and since then I have not been able to use my 4G, and my bars go in and out frequently. I have Straight Talk, my bill is up-to-date, and I don't really have any problems with texting or calling. I did a soft reset and wiped my cache partition and neither have helped.