I have read there is a virus going round and many children have it, also now adults do you get other symptoms ..any flu like aches and pains ?
I can relate to some of what you describe. I have asthma that got significantly worse over the past 2 yrs after a bout of whooping cough. You oxygen saturation can be in the normal range even during an asthma attack. Mine are always 100% even when I'm struggling to breathe--the docs can hear wheezing and the air flow improves after nebulizer treatments, but my oxygen levels don't drop. So, that's not always the best indicator that there is an issue. Also, your lungs may well be clear when you are not absolutely struggling--I have that issue, too. When I go to the doctor...I'm short of breath getting to the exam room--sit and wait for the doc, things settle down and my exam is unremarkable.
It seems like it might be worth exploring this further with your physician. Post nasal drip can certainly trigger asthma as can anxiety. Definitely things to pursue. Since this recently started, you can also become allergic to things after years of exposure, such as pets (especially cats), dust, mold, etc. Might be a good idea to be tested. Gastric reflux can exacerbate asthma and you may not have any symptoms of it (reflux)...you may not know you have reflux. There is usually a checklist of possible causes of asthma and the methycholine test for asthma isn't always definitive. A pulmonary function test would likely give more information.
Hope this is helpful. Good luck!