Should i be concerned?

My periods are irregular but the flow and how many days I'm on it stays the same. Well today's is the 6th day I've been on it which is also usually my last day. My period has been like medium flow but it seems like it's getting heavier. I can use a regular tampon for at least 4 hours before I have to change it and now i have to change it every two hours or I'll bleed through it. Also my back hurts me really badly when i get my period and i havent had any this month. I'm also sexually active and I'm not in birth control (if that matters any). Should I be worried or is this normal. Also I'm only 16 and have had my period for 3 years and it has never done this and on another side note i have been lightheaded on and off all day today. Thanks for y'all opinions in advance! I appreciate it! :)