Currently on oral steroids for asthma but still peak flow is around 350 and drops to around 260, soon as i got to work (clothing store) it starts off and continues all day and worked there 4 years now?

Asthma: Besides the prednisone are you on long acting asthma medications, rescue medications, do you have allergies that exacerbate your asthma. When you have an exacerbation like this do multiple triggers make you worse such as are found in the store you work in. Do you need antibiotics. You need to return and be seen your peak flow is awful, I wonder what your oxygenation is, and are you fit to work.

Occupational asthma?: Great that you are tracking with peak flow monitoring. Continue this mornings, evenings, at work and also on days off. Document it. If you are still recovering from a flare up such as after a cold then it could be any kind of dust, smoke or fumes including perfumes and off-gassing from new clothing that's irritating it. This may resolve once the flare is over. Continue inhaled steroids.