pressure during my period

   My started four days early which is unusually for me as I am always late ( period has been very irregular since it started ) anyway, when I my period started it started off brown, then changing to light red with small clots here and there ( sorry for the tmi ) but all day yesterday and one the 18th I have been feeling uncomfortable pressure inside of my vagina/cervix... the last time I had this I was referred to the hospital and nothing was found. 

Kinda wondering what it actually is as it is affecting me when I am working.