Beforehand, please excuse my ignorance in this field, as I am only beginning to delve into its astounding depths. So, as I understand it, Photons are the force carrier particles (gauge bosons) for the electromagnetic interaction (electromagnetic force). This given, one could pretty much say that EM fields are comprised of these photons and that all interactions which involve electric charges are entirely dependent on, and determined by, these photons (even if said photons are virtual particles as would be the case with perturbation theory-something my understanding of is extremely limited). With this in mind, when an electron repels another electron it is due to photon exchange between the electrons. Or when an electron is attracted to a proton it is also due to photon exchange. My question is this: What properties of a photon determine whether or not the particles between which it is being exchanged repel or attract each other, and to what degree that repulsion/attraction is? Additionally, I would very much like to improve my comprehension of perturbative models and how they explain fundamental interaction through virtual particle exchange, and so would be endlessly grateful if someone knowledgeable in such things would help me in this endeavor. Thank you all in advance.