Safari and SBBOD

I've been having trouble with Safari lately. Overtime I quit safari. The Spinning Beachball of Death pops up, and it keep spinning. So I have to force quit it. I've tried things like restarting my computer, clearing the caches, but non of them work. My computer memory is 4GB. the storage is 121GB and it still have 55GB of space left. My safari version is 8.0.6. The version is OS X Yosemite 10.10.3. It's a MacbookAir and the age is around 3 years. I hope if anyone could help me because it's really annoying and slow.