Painful areola and nipple on left breast

Hi all im literally in my 16 weeks n 4 days journey. I dont normally wear bra at home n yesterday when i woke up was the 1st that i felt pain on just my left areola n nipple. N when i touch it it is hard but it is not when im lying straight up.. its only painful when i let loose n when im in an upright position be it sitting or standing (without bra). Not when im lying down.. i hv to literally hold it up or rest it against my pillow to avoid from the pain..Nothing on my right breast though. I do not know if it has anything got to do with milk producing or its others that i should be concern of..Ive gone through the sore n tender breasts during 1st trimester but dis is nothing like dat. Pls advice me