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?

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.

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