Could be spider mites Adriane. Turn over the leaves and see if you can find little black specks on the reverse. Spray the leaves with neem oil and hopefully it will help.

I was thinking the same thing. They spread fast. Take off all the damaged leaves and throw them in your garbage (not compost) before spraying Neem. You can try hand washing with soapy water before spraying, too... Neem doesn't always work for mites. Just stay away from Sevin, as that will make the problem worse!

Good luck.