Breast tenderness and hard lump in armpit. Scared!

Any and all advice to calm my nerves would be greatly appreciated, as I have been dealing with this for almost 3 months now. I am a 27 yr old female, It all started when I woke up one day with VERY sore breasts. Very tender to the touch on both sides of breasts going into the armpits. Never experienced breast pain before, could not indentify any lumps throughout, but like I said it was pretty painful pushing hard on them, so I myself could not feel anything. I brushed it off thinking maybe I did something, and let it run its course and go from there. It was off and on for the next couple of months with the tenderness, and I had started to not feel good. Last spring I was diagnosed with Lyme disease after a tick bite and my symptoms I started to have now were pretty similar to then- headaches, dizziness, achey lymph nodes. And they were all off and on. Just like my Lyme. So I thought ok, must just be my Lyme flaring up. The only difference now was breast tenderness but I had read a few stories of people that experienced this with their Lyme as well. So I just went along with that. A few weeks later, I was shaving in the shower and noticed that my armpit was a tad bit irritated and red, and I could feel a hard nodule, fixed, and deep in my armpit. First time ever noticing it, so unsure of how long it had actually been there. And I could only feel it if my arm was raised, if my arm was down it was not palpable at all. So for some reason it didn't really alarm me. The nodule itself was not tender, my skin was just irritated. So again, I thought maybe it's just irritation from shaving and I was also using a new deodorant, OR maybe it's also something with my Lyme, as Lyme DOES cause swelling of lymph nodes. The only difference with this is that it was NOT movable. But I was so convinced that my Lyme was flaring up, that I brushed it off as well. So I made an appointment with my OBGYN for my breast tenderness, just in case. And also had an appointment with primary care doc for the flare up of Lyme. OBGYN felt around and said I had very lumpy, dense breasts and the pain is most likely hormonal, which is very common, told me to start keeping track of it with my cycle and if anything changes, to let her know. I told her that I hadn't been feeling well and that my lymph nodes were achey and what not but told her I also had Lyme disease and thought maybe that was the cause of it all. Anyway, she sent me on my way. Went to my primary care, they agreed and said "oh probably your Lyme" and put me on doxycycline. Fast forward a couple of weeks, breast tenderness goes away with cycle, so it worried me less, but the hard nodule in my armpit is still there, my blood tests for Lyme disease have come back FINE, my Lyme wasn't even detected! So now I'm starting to worry thinking this is all being caused by something completely different and feel like a fool! So my primary care doc has scheduled a CAT scan of my armpit since he could not personally tell if it was a lymph node or something else since it was deep in the tissue, almost like it is on my tendon or muscle. His words were "I don't think it is cancer but I would like to see what it actually is". My CBC blood work also came back fine and normal, but I know that does not rule out cancer. He also scheduled me to have a mammogram since I told him my OBGYN said I have dense, lumpy breasts. I'm glad he is being deligent and getting stuff done for me but I am just so scared of what the results are going to be! I know that lumps and bumps are common and that breast cancer is not common among girls my age, but I know that it DOES happen, and my anxiety is getting the best of me. The more I read up on "hard fixed lumps in armpit" the more scared and anxious I become. I am making myself worried sick, and I would hate to get the diagnosesof something bad, knowing that I put it off for a couple of months since we all thought it was my Lyme disease. And it would absolutely break my heart to tell my parents and family the news of something like that! Has anyone ever had a similar issue and it ended up being nothing horrible?! Please give me any insight. Thank you so much!