Yikes! I blame pregnancy hormones myself - they get blamed for everything else
I don't cough all the time with asthma, but if I get run down/get a cold it's the cough that's the most noticeable symptom, if you see what I mean. At that point I usually double dose the becotide (in preference to using ventolin constantly), on the recommendation of my GP I hasten to add, and continue that for a few days after "all is well" and then I can pretty much stop use until I start to get run down again.
In the winter when lots of bugs are around or hayfever season I might take "normal" dose just as a precautionary measure.
I do notice a fairly big difference within a few days of taking the Becotide.
Hope this helps
You might also find the National Asthma Campaign site helpful. In particular the Asthma and Women section (scroll down to the bit about pregnancy)