Is it possible that after a month of using Diemono tablets I have brown spotting?

Yes, brown spotting can occur and should not bother. Symptoms should disappear in the following months of use. According to the manufacturer: "Adverse reactions are more frequent in the first months after initiation of treatment with Diemono and disappear with continued treatment. There may be changes in the bleeding profile such as spotting, irregular bleeding or amenorrhea." If anything worries you, the situation should be discussed with your gynecologist. If you are not able to consult your doctor, you can use the teleadvice here: https://www.gdziepolek.pl/telekonsultacja/z-ginekologiem