T mobile Question. PLEASE HELP?!?

[Jessica]

About 2 weeks ago i got a phone.The Mytoch 3g Slide.It was working good until yesterday. Since the Morning. I keep loosing service Constantly. and i cant seem to send text or pictures although i hvae unlimited. i went to the t-mobile store and the guy that helped me said it was because my SIM card wasnt secured and that my problem was now fixed, But i doubt it beacuse if it was the SIM card then it would of happened since the day i got the phone, And my battery dies Extremely FAST. Whats wrong? Please HELP :/