Out of Memory?

Happens a lot. Happens to me in creative and survival because I never use the others. When it happens, the game part of Minecraft crashes, and it says "minecraft has run out of memory", then takes me back to the home menu. Sometimes it will only happen once, and sometimes it will happen twice. Today I was playing and it crashed, and I loaded my world, and almost immediately crashed again, and again, about 7 times, then I exited out of minecraft, and didn't have any more problems. Sometimes, it will crash twice or three times, and then minecraft will totally crash, and an error message pops up (included are 4 messages, I assume they are all from the 2 or three times minecraft has crashed like this, but they might not be).