My Ipod touch wont tell me when i have a notification on twitter or facebook?

well, one day i was bored so i decided to go play around with my settings, i was messing with the sound, but after i was done messing with it i changed everything back to normal and now my twitter app wont even tell me when someone messages me, re tweets something, or anything... my facebook still sends me push notifications but it wont make a sound... it did once but after that it stopped... can this be fixed? and if so could you tell me how? i would really like my ipod to work again...