Itchy red bumps on legs and spreading

I went to the beach this weekend and forgot to shave my legs.  Luckily I brought I razor along and on Sunday before heading out to the beach I shaved my legs.  Stayed at the beach for some time.  Laid in the sand splashed around in the water, even headed to the pool.  Later that evening I noticed tiny bumps on my shin.  I really paid it no attention that evening, but as the days went by the bumps spread covering most of my lower legs and the bumps which were once skin colored turned red.  Now, my skin is the color of milk chocolate, so this bright red has me kind of freaked out.  The bumps are itchy and I've been putting cortisone 10 to ease the itchiness.  The itchy bumps seem to have spreaded to my arms and now it looks like my breast and back.  

What could this be?  I have an appointment with my doctor today, but what should I expect him to tell me?  Has anyone experienced this before?  Please help?

[Dr_Aparna]

Hi,
This could be an allergic reaction either to the sun or to seawater or even the rough abrading quality of the sand on the beach.
When an irritant comes into contact with your body, your immune system sends chemicals, including histamine, to fight it. The sudden spike in histamine levels can cause an outbreak of bumps  in the upper layers of the skin.
The exact area targeted or the trigger which set the reaction off is determined by an individual's genetic predisposition.
You can take an anti-histamine for the rash and itch and apply Calamine lotion to the affected areas.