First thing to realize is that not all dogs are cuddly... and in addition to that, 5 month olds have a lot of energy and don't like to be still for very long. You are right in thinking you need to nip this i the bud, but it is your handling of the pup that will make the changes possible. What you describe is not aggression. Aggression is something the dog initiates. In the case you describe, the dog is reacting to your handling and more likely fearful of being restrained, than aggressive. If you hold a pup too long, you may get the same reaction, even if you are not trying to remove a tick, which is not in itself easy to do in a calm way.
There are many occasions in a dog's life when they need to accept restraint, such as a visit to the Vet, grooming, nail clipping, removing something stuck in the mouth, etc. . The place to start is to accustom the puppy to liking being touched in a calm soothing manner, while laying on its side. Do this at a time of day when the puppy is calmer and more relaxed and do it as often as you can, starting with a minute or so and gradually more.
As the pup comes to like this and trust your handling, teach her to accept your handling of her feet, mouth, ears, always in a gentle manner. Next hold her still for a brief moment ( you can say "hold still" as you do this) then praise and give a small treat, or throw a toy. This will teach her to know the meaning of your words and actions, learn to trust you, and learn that being restrained for a short period is not a threat. Training in this way will prepare the dog to accept your handling more calmly when you actually need her to ( like when you have to get a tick off ). Dogs are all different in the amount of handling they are willing to put up with and under what circumstances, but you can elicit the best from her by working with her and her individual personality.