I'm sorry you're panicking 
I understand that health anxiety isn't rational, but it must still be worth talking sense to it.
Sometimes it helps to imagine your anxiety sitting in a chair opposite you. I'm sure it looks nervous! Speak kindly to it.
Does it think it can see things the scan can't? How would that work, exactly? Look up the type of scans you had - CT, MRI, ultrasound, etc - and learn how they work. I find them awe-inspiring; it's amazing that people actually invented them to record the details inside people's bodies!
Ask your health anxiety why it doesn't believe them.
The professionals you saw have examined hundreds or thousands of breasts, all of them individual, some malignant, most healthy, some with other diseases. You and your anxiety have only examined your own. Who's more likely to know their stuff? You can only compare your breasts with each other. The professional has vast experience of people's breasts, with various health conditions, to compare.
Is your health anxiety scared of yours being compared with other people's breasts? I wonder if it knows why; can you ask? What makes it think you have a condition no qualified & experienced professional has ever seen before? How likely is that, really? Reassure it.
If your anxiety was right, what would it want you to do about it?? You can't really diagnose a mystery condition and then treat it. What's the treatment for an unidentified, unspecified problem, after all?
I am not a fan of this suggestion, but you might want to consider it: attempt a mystery treatment for a mystery condition. Use lavender and sage oil, burn pure beeswax candles while massaging in the oil or cream. Learn about breast anatomy and breathe slowly while visualising the healthy insides of your own. Ask your anxiety if it likes these ideas.
Sending you a hand hold and your health anxiety a friendly shoulder squeeze.