iMessage activation

i recently got an iPhone 5s, and have been trying to activate iMessages for several days. It either stops immediately and tells me to try again, or loads for a few hours and then tells me activation was unsuccessful. It’s not a problem with the carrier, as the other people on the same plan as me can send iMessages. I’ve tried all the things listed on the website, and it’s still not working and I’m getting really frustrated. What should I do?