Hormonal changes and growth spurts can play a big role. Depending on your age, that is probably the most likely answer. Other life changes play a big part: moving, changing your diet or exercise habits, changing your work shift (which affects sleep) can all play a part. Some say spicy foods cause excessive dreaming.
I don't think you're dreaming more rather than you're remembering them more often. Everyone dreams, except for rare cases where there's brain damage. I'm sure if you have a lot going on you could have more dreams.. rcw's answer looks pretty accurate :D
Actually everyone dreams about 6-7 dreams per night, but there are only 1 or 2 of which that we can remember. Unforgettable dreams occur especially when your brain runs excessively active before you sleep. BTW, sleeping with your arms on your chest will probably lead to nightmares.