I need to know how to dose my dog with antibiotics. She has mastitis because she tries to adopt every baby animal she comes across.?

That sounds like False Prergnancy, a hormonal condition, NOT mastitis. Put away the antibiotics. they won't help for this.

You shouldnt even have "leftover" antibiotics. They are meant to be taken until the full course is gone. I doubt you have enough to give the dog a full course, and even less likely that is the proper medication

Amoxicillin is available in 250mg and 500mg capsules. The recommended dose of amoxicillin in dogs and cats is 5-10mg/pound every 12-24 hours. Amoxicillin can be given with or without food as it is stable in gastric conditions.

Or 5 mg/lb body weight twice daily for 5 to 7 days or for 48 hours after symptoms subside.

Its illegal for anyone other than a vet to advise you or treat your dog. No one here would risk it.

If you are in the UK sign up for the PDSA. the vet care isnt free, but they dont ask for a large donation.

She could actually have a mammary tumour, so see your vet.

Call your vet and ask.

then ask your vet phone calls are cheap if not costless