Yes is the anwser, all meds for ED do this even herbal, you need to take a brake from Viagra, its best if you can find any of the other ED drugs and then rotate them, or change over to herbs, you could try the 5Gs, just google it and look for pegym, or google DRUGS VESUS HERBS, HERBS MY CHOICE, and follow the instructions that you find, its how I got over ED and now in recovery, but even with these I take a brake for a week and take for 5 out of 7 days, it works and it has to be come a way of life.
Good Luck
Most likely yes. After long term use of any drugs our bodies become more immune to the effects of them and so you'll find they don't work as well as they once did.