My phone's doing odd things

[MrPorky]

For the last few days, when I send a text it shows as "sending", sometimes for as long as 12 hours, other times for an hour or so. Then, eventually it changes to sent and shows a time somewhere between when I wrote it and when it changed to sent iyswim.

The recipients do seem to get the texts, several hours later and sometimes several times. The worst being 7 times, in the early hours!

The same seems to happen when others send me texts, I received three from different people at 1:40 this morning, I can't imagine they were actually sent then. I also received one this afternoon, which says 7:30 Sunday on it.

Is it most likely to be a phone or a network problem? What do I do?!