Mystery rash - contact dermatitis, poison ivy, scabies?

About 5 days ago I noticed what seemed to be two spider bites on the side of my right butt cheek.  They were swollen, red and itchy; later that day, I noticed another one above them (though I wasn't sure if I had missed it before or if it had happened in the meantime).  The next day they were considerably more swollen, red and itchy, and I had another rash on the front of my right thigh - they were blotchy, red, and itchy.  I also noticed one little spot on my right forearm, and one on my left front thigh.  
I had no idea what this could be...I started thinking it was an allergic reaction to a couple of spider bites, or laundry detergent, but it just doesn't seem likely because I've never had any kind of allergic reaction in my life.  
Then I remembered that my boyfriend said he'd come in contact with poison ivy about a day before I noticed anything.  He's immune, so he wouldn't have noticed it and didn't bother to wash himself.  Could I have contracted poison ivy from the oil still on his skin and clothes?  
I would like to think it is as simple as poison ivy, but the rash seems too sporadic for that, and doing research on skin rashes the last couple of days, I've become very worried that it might be scabies.  No one else in the house has this rash though...

[Here is a picture of what the rash on my right front thigh looks like.]

[BhumikaMD]

Hi,

It could be eczema, sweat dermatitis, allergic reactions or folliculitis.

You need to wash the areas several times with fresh water. Do not use any cosmetic products at the sites.

Apply calamine lotion at the site of the lesions and see if it helps. You could take some oral antihistamine medications like cetrizine or loratadine. You need to maintain a good personal hygiene .

Anti-itch drugs, often antihistamine, may reduce the itch during a flare up of eczema, and the reduced scratching in turn reduces damage and irritation to the skin.

For mild-moderate eczema a weak steroid may be used (e.g. hydrocortisone or desonide), whilst more severe cases require a higher-potency steroid (e.g. clobetasol propionate, fluocinonide).

Eczema can be exacerbated by dryness of the skin. Moisturizing is one of the most important self-care treatments for sufferers of eczema. Keeping the affected area moistened can promote skin healing and relief of symptoms.

Let us know if you need any further information.

It would be advisable to consult a skin specialist for the symptoms and a proper clinical examination.

Regards.