3 days ago I had my 9 week old kittens Pumpkin and Sweet Pea vaccinated. The vet asked if they would go outside in future or whether they would be indoor cats. They will be going outside and also be in contact with 2 older cats in the household. So my vet recommended she give them 2 shots instead of one. The vet said they might be off colour for a few days. Both went off their food a day later but Pumpkin was still playing and fairly bright. Now Sweet Pea has eaten and drunk nothing for 2 days and doesn't want to come out of her bed. When she does she is stiff, slow and lame. She feels very hot. Instead of feeling like a solid little lump she feels like a feather when you lift her up. I weighed her and she has lost weight from last week. I managed to syringe about 1ml of warmed diluted Whiskas cat milk into her mouth this morning. I put her in the litter tray and she tried to pee but because I think she is dehydrated not a lot came out. I really don't want to take her to the vet again in case she fills her with pain meds and antibiotics unnecessarily. If she is so poorly I don't think she would be able to tolerate anything else in her system and it could tip her over the edge. You see I am beginning not to trust this vet. She is a lovely person but she prescribed long term Metacam for 2 of my cats. One developed trouble eating, lost a lot of weight and later died of a multiple stroke, the other also developed trouble eating, lost weight and still is not right, yet she continues to recommend it even though there are a lot of side effects. I know kittens can be ill for a few days after innoculation. I want to nurse Sweet Pea through it without getting too panicky but I am worried that she will die of dehydration and I really want to do the right thing. How often should I give her liquids and how much at a time to keep her hydrated?

Optional Information:
Pet's Sex: Female
Pet's Age: <1

Already Tried:
Keeping her warm and quiet. Syringe of warm diluted Whiskas cat milk. She took about 1ml - 1.5mls before refusing any more. She washed her face afterwards and seemed a little brighter. I have tried warming chicken Felix cat food in gravy, mashing it up and giving this but she refuses it.