[Sun Care] Why do I run out of sunscreen so quickly? Is this normal?

Beauty Tips For Body Care
Some of the other sunscreens I've used have lasted longer (like a month or more), but my 50 ml container of La Roche Posay Shaka Fluid lasted TWO WEEKS (technically 13 days). It's very liquid-y, which may be a part of it, but still! It's especially frustrating because I paid a little more for it (I live in the US and buy the French version, so I have to pay for int'l shipping + a premium).I DO use a lot (not more than what's recommended, though—about a shot glass's worth) and reapply often, but you're supposed to! I love the Shaka Fluid and would love to keep using it (because its PPD is so high, and European UVA filters >>> American), but this isn't financially sustainable. Can anyone relate/have any advice? I would be open to Asian sunscreens too—they're also better than American ones—but I'm paranoid about buying a fake on Amazon, eBay, and similar sites.
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Submitted by bitchcrisis