Iphone 5c sprint going from 4g to 3g?

I got this phone monday and ever since ill have 1, 2 or 3 bars sometimes itll be 4g 2 mins later its 3g which is much slower then 4g can i get some help?

Sprint still doesn't have enough 4GLTE antennas. 4G barely launched in 2013 so its still building. There are still many many more 3G antennas as opposed to 4G, its something were going to deal with for the coming years till we catch up with Verizon.