Suggest Treatment For Unusual Spotting And Heavy Periods

hi i am a 29yr old 5'4 in height weighing 52kg. i am not sexually active but i have been experiencing some unusual heavy spotting for over a month now. earlier this year i noticed that my nature of my period changed and i get really huge clots of blood about 3-6cm in diametre. my cycle is normally 28days with normal flow but the last two cycles have been extremely heavy flow accompanied by pain and discomfort especially on the first day. 4moths ago i had an ultrasound scan done and everything was normal. 8days ago, after a month of heavy spotting and sometimes unusual blood color(blackish brown), i went to see the gyna and another scan was done. the results of everything were normal. the gyna put me on Primolut N, 5mg twice daily but till now the heavy spotting has not stopped. infact two days ago i had very heavy bleeding that looked like my period. any advice on that?