What Causes Irregular Periods And Tender Nipples While Sexually Inactive?

Okay, I'm 18 not sexually active at all. Never had sex in my life. My nipples are always very tender even when I'm not on my period. Today, I was checking my breast out and clear liquid came out of one nipple and I tried on the other and it did the same. Once, I did this some of the pain went away. I'm also due for my period in about a week, but my period the pass 4-5 months have been very irregular. Last month I had my period for almost 2 weeks,and it was light. The month(August) before I had no period at all. July I had a light period and it was early. June my period was normal, but 2 weeks late. May my period was heavy, 3-4 days late. I do not know what is going on with my body can someone please help???