Hi and thank you so much for this query.
I wish to congratulate you on adopting a contraceptive
measure as a means to prevent unwanted or unplanned pregnancies. Keep up. I am so sorry to hear about the brown period like discharge and all the troubling thoughts of pregnancy
going through your mind.
No contraceptive method is 100% effective at preventing pregnancy. if you had unprotected sex, then you run the risk of being pregnant. The brown discharge may be as a result of an infection or something other reason. Since it has been at least 3weeks after your sexual intercourse, you may want to do a urine pregnancy test to figure out whether you are pregnant or not. If you are not pregnant, then we may want to gather more information from you and find out what the exact cause is if it persists, increases in volumes, becomes offensive or associated with new symptoms like pains and fevers.
Also, even if you were pregnant, it is too early right now to feel any firmness in your lower stomach. You may just be being too suspicious as you rightly suggested.
does not prevent against STDs. Always try and use protection during intercourse. this prevents against infection and also serves as a backup to the contraceptive method you are using.
I hope this answers your question and provides enough information fou you t make informed decisions on. I wish you good health.