Yes, it is possible to get Mono again. Also it is possible to get thrush after the use of an antiseptic mouth wash, especially with over-use. Thrush is an over growth of a yeast that is normally found in the mouth, called Candida albicans. Often this causes white spots of the tongue and mouth that generally look like cheese curds. The white spots are not always easy to see. Sometimes just redness is seen. Sure, healthy people can get fungal infections in the throat, if they are "run-down", taking an antibiotic or using a steroid inhaler for asthma or COPD.
This is all purely speculative without having a throat culture done. Thrush usually shows up with white patches, so I've been told, although I'm not a doc. We just get the swabs in the lab.
Did your previous sore throat present with white patches? Mono eight years ago really doesn't mean much now, I wouldn't think. Have you been on any antibiotics recently? This can cause overgrowth of yeast (Candida albicans) which is the usual cause of thrush. I have no answer to your mouthwash question.
What is your age? You really don't give a lot of other pertinent information that would help. It would also help if we knew your sex and any history that would be significant. When I work up cultures (I'm a med tech in microbiology) I always look at age and sex of the patient, along with preliminary diagnosis, which is on my screen, to guide me in the workup.
I am a female, late 20's, HIV negative, light smoker. I have not been on antibiotics at all lately. Does that help with anything?
I'm glad you mentioned your HIV status. Overgrowth with yeast or fungus in the respiratory tract is sometimes associated with AIDS/HIV. However, since you haven't had a culture done on this one, it could just be a viral or bacterial sore throat.
(I posted this one for the pics at the bottom)
(This site has pics and some good information on Thrush as an STD)
(This is a link to a Google Image search for Strep throat. Other Strep groups besides Group A can cause sore throats in young adults. Group A is the group associated with rheumatic fever and kidney problems, so is taken more seriously by the medical community. Group C, however, can cause a lousy sore throat in young adults.)
(This is a view of a throat from a Mono patient).
It's best not to speculate and have a doc look at your throat.