I have not ever taken Lexapro, so I don't really know, I would think that being on it only 7 days however would not give you this reaction. Ask the pharmacist, he should be able to help.
I have "stomach flips" I actually discovered, for me, they are gas bubbles causing my heart to do the "flip flops" they are called PAC's or PVC's and are usually benign, but they are very annoying. Lots of folks that are nervous have them.