sore boob ! 😭

Okay so I had sex the week of the 3rd-11th (June) and like my period was two days late . It was supposed to come on the 19th but it ended up comin on the 21st and staying in for five days. Yeah it was late , but it came and I cramped and bled normally. I'm still spotting alittle but not heavy bleeding like my period . I just got off my period a day ago and like one of my boobs has been hurting . It's not like unbearable but it's irritating me . Like and it's way warmer than the other one when I touch it , and to make things worst there's like this little knot under my nipple ! I heard if you got your period then you can't be pregnant.. but people have been telling me you can !Every time I google my symptoms and try to figure out what it is I'll end up scaring myself because it'll tell me pregnancy or cancer or infection or something crazy like that.. I'm so confused and lost and this will make the second day my boob has been sore . Any advice or help? Like I'm planning on taking a pregnancy test to ease my mind and help me find peace but I'd rather hear what y'all have to say . I'm only 18 if you guys wanna know my age . And if it happens to be anything serious I'll go to the doctor .