Why have I suddenly developed hayfever? It started on Monday and initially I thought I was getting a cold but it clears within an hour if I take antihistamine and then starts t return about 15 hours later. I have had mild hayfever before and I’m allergic to straw dust (I haven’t been near any recently) but this is more extreme - feeling really blocked up, runny nose, sore swollen eyes etc. I’m mid 40s if it’s relevant.