Welcome to the forum.......There's something not right here! Do you trust this Vet? Have you used him/her for any length of time?
I have to ask:
Was the vaccine given before the snap test or after? Thank you......Karla
I really feel it might be wise to give the Doxycycline as prescribed, twice a day.Lyme is difficult, though not impossible to treat, and you want to clear this as soon as possible.
You could always try the prescribed dosage and see how he goes. Sometimes some dogs can tolerate medication quite well, without too many side effects, even though side effects might be expected. Mine does.
However, if yours has a history of GI problems, or is a poor eater anyway, or has history of liver, kidney or pancreas problems, you really should discuss this with your vet.
In fact, there would be no harm in discussing the Doxycycline reatment and your concerns about side effects with your vet anyway, and it would be perfectly in order to call the vet's office, ask if there is a time during the day you can speak to your vet when he is not busy. No doubt he will call you back when he has a moment to discuss the treatment with you.