So I have developed a new obsession due to trying to stop another. Most of my obsessions/compulsions revolve around the number 4, and in trying to break those, I now have an obsession that I must avoid the number 4 at all costs. Same with any number divisible by 4. Any advice?

An ERP example would be to not avoid the number or any related numbers and sit with the feeling of anxiety for least 5 minutes. Then you gradually sit with the feeling for 10, 20, 30 minutes. Until it doesn’t feel as distressing. 

Just remember to not overload yourself. It’s more a gradual process 

I used to have that exactly. I would add up numbers or count stuff just to see if the result divides by 4. Microwave number had to be divisible by four. I stopped though, and how I did it is by stopping the counting once I realize I'm doing it, consciously lose any good or bad meanings I associate to the number, if I choose a number such as with the microwave, I choose any number, etc. 