I had that problem in the beginning, STB. Back in the early 90s, when I got hooked on Thai food, I must have checked 20 or more brands of fish sauce, and tossed all but a half dozen! Fortunately, back then, these were all something like $1.29 or $1.39 each! Funny thing is, the more expensive brands were what I call the "fake fish sauces", which don't need as much time aging. You can identify these because, in addition to the basic ingredients of fish, salt, and water, they will have others, usually including hydrolyzed vegetable protein. These "age" the fish with enzymes. Same with many soy sauces, that you'll see these ingredients in, and the flavor just isn't as good.
The best brands I have found are these:
Red Boat - the "40" is their cheapest, and good for most dishes, cooked or raw, uncooked. There is a more aged, sweeter, more expensive version that I don't use for much, except raw, milder flavored dips, where the flavors come through.
Tra Chang - the regular, cheaper version, was my favorite, back in the 90s. Strong enough for cooked dishes, but also good in dips, and other uncooked dishes. The Gold Tra Chang is something I only found on importfood.com, and if I had to pick a favorite, this would be it. Stronger, but balanced, and still good in raw dishes and dips. You know this is good - the only thing on the label in English is the nutritional information! The rest is in Thai!
Golden Boy - Mild brand, that I used only in some dips and uncooked foods.
Tiparos - this was ok - borderline, as far as having a "raunchy" flavor, but good in curries, and things that cook a while, because the off flavors, in these and some other brands, cook off. And the Asian markets used to give these away free sometimes!
Many of the brands that the chefs and authors touted back then, were absolutely horrible! My friend wouldn't throw them away - he would use them in a dish that would cook a while, which cooked the bad, volatile aromas off, and the dish would be ok! But his whole house would smell like it, and his wife threatened to throw him out if he used them again!
My theory was that many of those fish sauces were much fresher, out west, where those chefs and CB authors got them. And by the time it got here, on a cargo ship, was months later, exposed to a lot of heat, and just wasn't good. And maybe you have that problem in Israel, where you are STB.
Despite what some say, fish sauce should be refrigerated, once opened - I learned early on that it goes off eventually, at room temp. So I refrigerate mine, even before I open it. Never had it get bad since.