Why can't I receive any texts?

[strawberryabc0]

Ever since I got my ZTE Valet back in February 2014, there have been occasions when important text messages have been either delayed, or not come at all. Phone calls haven't been affected. This seems to have increased within the last three weeks. Some examples of this: last week, I got a message 6 hours after it had been sent (we compared phones) and today I didn't receive a very important text message at all, that was sent at least 24 hours ago. I'm wondering if it has something to do with the fact that most of my friends have iPhones, or whether it has something to do with the network. My phone is not rooted, if that helps. I use an app called Contacts+ instead of the base messaging app, but I have tried using the base and it is happening there as well. I also have some problems with the time showing up correctly. Often it is anywhere from 11 hours to 10 minutes off, and will not correct itself until I restart it. Thank you so much for your help!

 

[strawberryabc0]

I forgot to mention that I have wireless on while said texts were sent, so I don't believe that is the problem. The data signal strength is also strong.