lump on puppies stomach

Question
I have an 8 week old black labrador that we just got last week.  We noticed a lump this morning on the left side of her stomach.  It wasn't that big.  It has gotten bigger as the day has gone on. It is is skin color w/ a small red dot in the center and about .5 inch wide.  Sorry to ask you such a detailed question.  Just really worried and haven't been able to find much info on internet.  She was just de-wormed earlier this week.  We are going to try and take her to our vet on Tuesday because they are closed tomorrow for Labor day.  Didn't know if I should be worried and take her to an emergency vet before Tuesday.  Any advice you can give would be appreciated.  Thank you from a worried new dog owner.

Answer
Hi Matt!

I don't think it's anything that won't wait til Tuesday. You said it is on the left side of the stomach, so I will rule out a hernia, which would be where the "belly button" would be located.  It sounds like either a bite or sting.  It is probably swelling.  It is safe to give your dog Benadryl if you want to ease the swelling and/or itching.  I am going to copy and paste the directions here. Please read carefully.
God bless!
Becky

Benadryl for Dogs or Cats

Benadryl is a brand name for an anti-histamine (diphenhydramine).  Although it is considered fairly safe for use in dogs and cats,  please be aware that it does have potential adverse side effects.  It may interact with other meds that your pet is taking, so do not use it without first consulting your veterinarian. You should also use extreme caution using Benadryl in dogs that have glaucoma, prostatic disease, cardiovascular disease or hyperthyroidism.  

Benadryl is quite effective when used in proper dosages.  
Stops itching
Controls vomiting
Good for motion sickness
Can be used as a mild tranquilizer
Good for snake bites
Useful for vaccination reactions
Good for bee stings and insect bites

Be sure to use only the plain Benadryl formula. Giving benadryl with other combination of meds could be fatal, so be sure to read the box.

Liquid Benadryl is too high in alcohol content to be safely used for animals.  Please use capsule or pill form.  

Dosage every 8 hours
Dogs under 30 lbs and Cats :  10 mg
Dogs 30-50 lbs:  25 mg
Dogs over 50 lbs: 50 mg