Of course theres an alternative why would he say that? theres so many flea and tick medicines out there i'll name a few..
http://www.k9advantix.com/ http://www.revolutionpet.com/default.html
I use Proticall...
http://www.healthypets.com/prinfordo.html
and then theres a few cheaper brands like hartz
Maybe its an allergic reaction? My chihuahua is allergic to Proticall..so we don't use any meds on him. Have you checked the symptoms of allergic reactions should be on the box

?
I hope your furbaby feels better
edit: you said you also give muffin half dose? is she okay?