Breast pain

Hi ladies, 
​Am after some advice!! Have noticed recently that's left breast has been quite sore.... Usually around time that AF due... But this month have noticed it's quite sore to touch and also feels a bit harder than the right.
​Am actively TTC and am now 4DPO so I don't think it's related to that... Too early...
​Just wondering if you think I should go get checked out? Or leave t a bit longer and stop poking it!? Haha!!
​It hasn't changed shape or size.... Just sore. And just one sided!!
​Advice greatly received!!!!