Buy more?

I've been holding some Eth for over 3 years now. Bought it for cheap and now it has given a good return. But the past 1-2 years I didn't have a job and couldn't invest more, I finally got a job and have made some savings so I can start investing again. Problem is I'm not sure if I should invest now or wait for a dip. What if the dip comes way later. Suggestions?