Brown discharge 12th week

On my 12th week day 4 now. I have brown light spotting discharge yesterday, size of a 20 cents coin. I usually have either white or yellow discharge, but yesterday brown discharge with no cramps or pain. I went down to KK A&E today and was prescribed with 200mg Utrogestan for 2 weeks and ultrasound scan was normal. Should I eat the Utrogestan immediately or should I continue to observe since I only got 1 day of brown spotting ? Is there any harmful side effect to the baby or myself in the long term for eating this pill?