I have a 4th generation IPod touch and IMessage and it won't let me get pictures/videos from my friends?

I have a 4th generation IPod touch and it has the ios 6.1.6 and when ever my friends try to send me a picture or a video I can't get it and when I tried turning it off and back on but that doesn't help at all and I'm tried of the pictures not coming up, the one day my friend sent me 3 pictures that I didn't even know about. Please I really need help!