JulesPat - welcome to MM - you haven't told us your age and what is happening with your periods?
It could very well be early stages of peri meno - the hormones will be fluctuating and this can happen on and off for quite a few years. Do read up all the info on this site to get clued up.
Early side effects of SRRIs can be distressing and, like anything, finding one that suits you is trial and error I believe.
If you are suffering with meno symptoms then the SRRI is not the right treatment - hopefully bloods were done before the GP prescribed them. Thyroid function should also be checked.
Keep posting DG x