Irregular periods, i've been menstrating 4wks & my flow has gotten very heavy the last few days, feeling lightheaded and tired, should i be concerned?

Yes: Prolonged bleeding and heavy bleeding can lead to anemia which puts stress on your heart and decreases the ability to carry oxygen to all your tissues. You need to be seen ASAP either by your PCP, your GYN, an urgent care clinic, or an ER. Then look into what is causing the bleeding so it can be corrected and doesn't happen again. Hope this helps and you are feeling better fast.