Dark brown discharge

Please help po, ask ko lang po bakit po parang may old blood pa po na lumalabas sakin? Normal po ba yun? Im on my 24th week. Tuwing iihi ako, mejo mahapdi, tapos may blood stain yung undies ko, dark brown po kulay, pero wala naman pong kasamang sakit ng puson. UTI po ba to?