To make saline solution mix one teaspoon of non-iodized salt with about 15 ounces of warm water and let it cool. Alternatively, contact lens solution works well, and so does 'H2Ocean' mouthwash. Never touch your piercing with dirty hands, and NEVER use cotton buds. Fibres can get into your piercing, encourage infection and prevent healing. For a monroe piercing you could soak a piece of kitchen roll in the solution and hold it on for a minute or so. Or douse the piercing in it. Also swish some around in your mouth to deal with the inside wound. Another handy tip is using a shot glass - fill it with the solution and put the piercing inside for a few minutes. This is very effective and you should clean your piercing like this after every meal. You could also use non-alcoholic mouthwash. Don't use creams like savlon - they don't work on piercings. I don't know why your piercing is infected but you should just follow aftercare instructions you've been given - if nothing improves return to your piercer or seriously consider removing it.
Remember not to overclean as this is as bad for a piercing as not cleaning it at all. If it swollen then take some anti-inflammatories like ibuprofen and use ice to cool it. Also, with facial piercings is it recommended to cleanse your face twice a day with an-antibacterial pH balancing soap with lukewarm water. If I didn't answer your questions then feel free to ask, piercings have become kind of an obsessive hobby of mine, ahahaa. :)
Make sure it is non-iodized sea salt. mix it with a bit of warm water and apply directly to the infection