Well seeing as I have a nebuliser at home, I would go if it sticks around 50% after nebs or I am feeling terrible with it (blueness and sweating ect).
Your peak flow is 68% now, which is quite low, but not really an emergency unless you are feeling awful. Have you doubled up your inhalers/ started steroids?
You may want to have 2-3 puff od blue inhaler every few hours to keep on top of the wheezing, and double the dose of your preventer if not taking oral steroids. Also do you have allergies? If so take an antihistamine every day. HTH