If testicular cancer goes untreated, do the symptoms get worse and more obvious within months?

If you suffer from testicular cancer, you should be properly treated for it asap. Neglecting this problem can lead to a very serious outcome with additional symptoms and problems. See a urologist or other cancer specialist asap.

Yes, Testicular cancer is one of the faster growing Cancers. So a delay of several months is likely to make the cancer bigger and have the related consequences of increase in symptoms and risk of spread(Metastases) to other parts of the body(Abdomen and chest)