What Causes Flushing And Headache After Taking Progynova?

HI, I have just had a TAH 10th March due to giant fibroids. I am feeling well enough physically even though I have a wound . I have decided to start on the Progynova 1mg today that my OBGYN has prescribed as I have been flushing, sad and headachy. My husband asked if it was too soon but i m not sure. I m 50 and have suffered some anxiety and a lot of stress and I don t want to feel crappy anymore. I also take St Johns wort daily is it still safe to take along with the HRT. My Dr is aware I am taking it, however HRT pamphlet states a question about it. Thanks so much, sorry so many questions.