i am having problem with my iphone 4S speaker. apparently, i can hear ringtone and alarm, but i cant seem to play music on speaker. HELP!

i dont know what happened to my Iphone. I cant play music on speaker anymore. and when i pressed on volume up and down buttons there is no show of increased or decrease sound. i need help. but i can listen to music and adjust the sound while i m on earphone. and i can hear ringtone, alarm and all. just the problem with playing music. THANKS!