wow your poor betta!!!! poor boy sounds like he has several illnesses. First of all Does he have a heater because they need a heater to survive and in his case if he does not have one he probably will not recover. Water changes need to be done regularly in a 1-2.5 gallon 50%-100% changes need to be done 2-3 times a week. Larger tanks of 5 gallons + need weekly cleanings of 50%.
Okay just thought I would address the above issues, you may already do all of this but I was trying to find a cause of the illness. Okay treatment, sounds like he has mouth/body fungus, if you have a heater raise his tank temperature a few degrees (no hotter than 28-30 degrees Celsius) gradually over a few days. Treat with a fungus medication such as malachite green. Swollen eye may be bacterial so either after completing the fungal treatment try something like methylene blue or mardel maracyn two to deal with the bacteria or try a multi cure that contains both malachite green and methylene blue.
As to the lump maybe just an injury otherwise the multicure may help but I am unsure about that. All I can suggest it keep his water really clean and keep him warm, if you do not have a heater at least wrap his tank in a blanket at night to help with insulation this is a temporary action but he really does need a heater I cannot stress that enough, but then you may already have one?
Good luck with him
, adding some stress coat may also help him and always be sure to use water conditioner when doing water changes so that the toxic substances are removed from the water to make it safe for him.