Hi, If really all STDs are excluded (please note that some tests have a “window period” before they become positiv) your condition might be not connected to your adventure. Have you self-tested your testicles? If not, do so: under warm conditions (to avoid scrotal contraction) feel your testicles through the skin of the scrotum. They should have the same size and feel smooth. On the lower and upper end there are sensitive structures attached to them that also feel smooth. Should you notice anything more solid please see a urologist for a sonography of your testicles asap. Otherwise see you GP to get a general check-up with a look at the situation and some lab work. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Alexander Davis, General & Family Physician