Its normal. Most likely its Confirmation Bias.

Think about all the other times you look at the clock or anywhere and the number was NOT 333. You dont remember seeing other numbers because your mind is fixated with 333.

You encounter LOTS of different numbers more than you think. What probably happened was you saw 333 for the first time, thought no big deal. Then on another occasion by coincidence you see 333 again and this time you remember seeing that number before so the number becomes "significant". So each time you see 333, the significance grows, you keep reinforcing the idea you are seeing this number a lot. But if you made a mental note of all the numbers you come across in a day, week, you will find the number 333 is not that special. It's just that your brain took note of this number and kept alerting you whenever you saw it thus making you feel like you are seeing it a lot.

Pay attention to another number like 44 and you will start seeing it everywhere.

This happens to me except its number 15.