TTC on Citalopram

My doctor prescribed me 10mg of Citalopram daily for my anxiety & depression. I have been on this medicine for about a month. My period has been regular since may (since my miscarriage) & I haven’t been late once. I am now a week late but, I’ve taken 3 pregnancy tests & all are showing negative. Is it common for your period to be late when taking this medication?? I’ve looked it up & it is saying this is a side effect but I just wanted to see if this was something common.