What happened to my LTE?

I went Santa Monica Pier like 2 months ago to go play pokemon go. As soon as I got there, I did not have any service. I restarted my phone and it said that I was at 4g (my phone is 4g LTE). I thought it was because I had barley started it up but my phone lagged a lot through out the day. Ever since that day, the 4g LTE has not appeared. Is there something I m doing wrong or could it be that I ve been using a lot of my data?