Thick yellow nipple discharge

Should I be concerned about this? My boobs have been a little tender, today I massaged them, and squeezed them a bit, and some thick yellow discharge came out. I’m not pregnant as far as I’m aware (period was supposed to start today, I’ve been spotting a tiny bit of red and brown blood since last night, took a test last night and it was negative)

The discharge from my left boob was super thick, almost like a solid, or oil when it’s cooled down. The discharge from my right nipple was thick, but more of a syrup consistency. I did breastfed for almost 4years, and stopped 6 months ago. I have some health issues (ehlers danlos, and POTS) as well as some mental health issues, including health anxiety, so I’m worried about breast cancer, but I also know I overthink and over worry, so I really don’t know how much I should be concerned right now. I have an appointment with my doctor in 2 weeks (for a different reason). Could this be breast cancer? Or am I overthinking? Could this be an std? (I was sa 6months ago, I was last tested for stds 3 months ago, all neg. That’s what my appointment is for, it’s actually the last testing I have to get done) here are the photos

From my right breast

From my left breast