How to deal with foul fishy odor of frozen shrimp
Shrimp, but also seafood in general, should not have a strong smell. You should be able to smell a faint salt water scent from them when not frozen, and basically nothing while they're frozen. If they're smelling a lot, that's a sign they may have gone bad.
It's impossible to say exactly what went wrong with them. If it didn't smell when you bought them and froze them, my best guess is that you defrosted them in an unsafe way. Always defrost in the fridge or under running cool water. Never leave them out on the counter (especially not over night).
I will also point out that your cooking method seems like a bit of overkill. It's very easy to overcook shrimp and have them end up rubbery. Just pan frying is perfectly sufficient. There is not need to boil them first. Overcooking can cause a strong fishy smell in seafood as well.