Trackpad acting erratically, diagnosis?

Hi! A little background on my machine... It's a chunky white unibody MacBook, made around 2010 according to the About This Mac. I bought it secondhand from a high school who had Apple-certified technicians working on site, so it was well cared for. They replace their laptop fleet every 3-4 years so when I bought it in 2013 it already had some use on it. It's rather old today, as can be seen (and heard) in the louder clicking of the hard drive, the cracking plastic on the hinges, louder fan and "Replace Soon" battery status. However, 2 days ago the trackpad began to act wildly, despite not being dirtied or having any liquid spilt on it. It began to highlight and zoom, open dictionary constantly, and resist movement in any direction it didn't want to sporadically jump to. This went on for several hours to varying degrees of awfulness. After cleaning the trackpad, pressing down on it and shifting it over a tad, and letting it rest closed while I slept, the next day was better. Occasionally it would act up for about a minute, but mostly remained fluid and usable excepting the right side which remains stiff and laggy. Today it is the same with occasional behavioral issues. Im worried it may be the battery swelling, but there's no way I'm covered by any warranty now after technician tampering at the school and years off of any plan. As well, I can still click both sides and theres been no key issues, so perhaps its something else. What do you think it is? If it is getting better, will it go away eventually? And if it is battery swelling, would it be better to just junk the whole thing and upgrade? This thing doesn't have a whole lot of time left anyway I'm afraid...