First off if you wear contact lens the most likely cause is ongoing irritation from the contact lens. Recurring infection, irritation and redness are a frequent reason for people to have to stop wearing their contact lens.
Second there are things that cause recurrent eye infections: rubbing or touching your eyes frequently, certain problems with the eyelids or eyelashes, a chronic eye infection of the eyelids (blepharitis), chemical irriation (like people that work in smoky places like bars and casinos), people that have dry eyes.
Allergies can often simulate an eye infection. The main point about allergy is less matter and more itching than an infection.
Lastly there are people that just seem to have recurrent eye infections with no "good" reason. It's like some people never get colds and other people have 5 or 6 or more colds per year.
There are problems with using antibiotic eyedrops for a long time (super resistance of bacteria) so don't take medications except as directed by your ophthalmologist.
JCH III MD Eye PHysician and Surgeon