Am I allergic to dust?

Last week I decided to clean out my entire room. I started off by throwing out all the old junk underneath my bed. About five minutes after cleaning under my bed, the top of my arm became itchy which later turned into a small red lump. Today I helped my sister clean her room where I did the hoover under her bed. I now have a small red lump on my elbow. Im not sure whether or not it was the dust but if anyone else has any ideas what may be causing this lump please share them thanks.