My lower back hurts after excercising (body pump class). How long shall I not go to the class, n what's a good cream (tiger balm?) to use?

Pain free x 2-3 days. You shouldn't return to exercise until you've been pain free with activities of daily living for at least 2-3 days. Then, do so gradually and avoid painful exercises. I don't find over-the-counter topicals very effective, especially for low back pain where the source of pain is rarely very superficial. Oral anti-inflammatories tend to work more effectively.
Good to exercise but. Listen to your body. It is ok to be sore in your muscles. Is not , to be sore in your joints. Adjust what or how you are doing the activity if it is making your joints sore.