It sounds like you both should be seeing an allergy/asthma/ dr and not just a GP. An allergist can make a huge impact on your quality of life.
we seem to have the same problem. my peek flow is around 220. in my experience when the doctor says they chest is clear it means there is no infection. I had to have weekly check ups with my surgery nurse because my peak flow was so low. Your G.P should really be discussing perhaps a change in medication or frequency of use of inhalers. Ive been an athsmatic all my life and at the age of 45 they are now trying different inhalers which are having good effect.
You should stay at the hospital. Of course 150 is relative to your personal best peak flow, but that is very low and most likely below 50% which is very dangerous.
Many people in severe asthma flares will "sound" clear because they are NOT moving ANY air so there is nothing to make any sounds.
Have the hospital check you pulse O2 with you moving if it is normal with you at rest. It is likely to plumet.
Keep us posted and feel better.