Probably not pregnant but I don't know what it is

[McintoshAmber]

Hi, this might be the most desperate thing I've ever done. I'm messaging because I have some worries about my condition. I don't even know if talking here would help. I plan on going to the doctor as soon as I get paid next week. I'm only 21 and I went to bed with sore tender breasts thinking it could be a sign of my period approaching. I woke up with my right breast noticeably larger than the left and its tender to the touch. I took a pregnancy test and it was negative, I plan on taking another in a weeks time just to be sure. My right breasts nipple has become red and is mostly all the time errect. I don't have any unusual bumps or lumps anywhere by my collarbone,armpit or breast. My nipple has no discharge but is extremely sensitive and not dry or cracked . I've googled plenty just out of concern until I get to see a professional who would probably be best to talk to. But I hope this is okay. I guess what worries me is how sudden it happened and how noticeable it is, my mother and sister and boyfriend barely looked at my breasts for second,third and fourth opinions and told me it looked bad. Its not swollen red or anything it looks like a boob but it's practically sore as hell and grew badly overnight with the sore nipple to put a cherry ontop of it. I've been having some serious worrying symptoms today which made everything worse. I can't sit upright or stand without feeling like I'm having difficulty breathing it feels like it's becoming a struggle breathing or like my breaths isn't sufficient enough. It's followed by nausea and a really terrible fatigue I can't bare.