My 40 days old puppy had loose motions and the vet gave him injections (antibiotics), a day later he had 103.5 °F (39.7 °C) fever and again got the injections, screaming in the process. Should I see some other vet, is it okay to give so many injections to a pup? In total he has had 5 injections in two days
Your question is badly fomulated. You are in a way telling us your dog has got too many injections, but this is definitely not the case for your puppy.
Two of the injections were antibiotics; this is very common if the first type of antibiotics had little or no effect and this is how a good vet will try to help your puppy.
Two of the injections were most likely subcutaneous fluid and this is the way dehydration is treated when yor pet has diarrhea and it might be better to treat it this way than it is to give IV fluids over night.
The last injection was most likely a painkiller to get the puppy's fever down. All of this are common treatmens that your vet will give your puppy.
So I cannot see your vet could have done this in a different way, your vet could have been better at informing you, but not all vets are good at this.