A few weeks ago my headphone port starting acting temperamental and only played audio if I held it at a certain angle (or weighed it down with something to keep it at that angle) but it has now reached the point where that doesn't work. I ordered a USB sound card on amazon but it's mono and has NO bass.

Anyone know what alternatives there are? Should I just invest in a better USB sound card? Should I take the laptop somewhere to get it fixed?

It happened to me too, ain't no way to fix that

Take it to a repair shop and they should be able to fix it

Maybe it can be fixed, maybe it can't (at a reasonable price). You can ask a repair shop to take a look first but I think it can get quite pricey. A higher quality usb sound card would probably be more practical, you might end up with better sound than you had at first and at a better price than fixing the port.