Why do I have 0-2 bars on my boost mobile phone?

I got the sanyo incognito, I read and watched loads of reviews about it and it's a pretty good phone. So I got it today and they activated it right at the radio shack and I made a call and it worked fine! I even IMed on it on my way home and it worked fine. But now I'm at home and I have like no bars, I've been texting and it's been working fine, but now towards the evening, its working worse. I got a text from my friend at 8 oclock, but it was sent at 6. It was 2 hours late. I called my phone from my house phone and it didn't work. What's going on? I got a cdma phone and I live in a city area. Is this just for the first day? Help.