Question about mastitis?

Nope, sounds nothing like mastitis. Mastitis will typically present with a rapid-onset moderately high fever and body aches, headache, chills, and pain the affected breast. (Often you go from feeling perfectly normal to feeling intensely ill in a matter of hours.) Sore throat would not be typical at all. The fact that you started with the sore throat and now have fever, chills, and aches makes me wonder if you might have strep. You might want to check in with the doctor on that one.

It could be. Are there warm spots in either breast? I had it with my first born, she was 3 months. I have never felt so terrible in all my life. Sore throat, headache, fever, muscle aches, back pain, chills, it was terrible. The only relief is a warm/hot compress to the affected area, and continuing to breast feed and or pump until the blockage dislodges. It wasn't super super painful, but very very uncomfortable. But a warm spot in the breast is a good indication of which side might have the blockage.

I'd suggest contacting your OB/GYN. It likely could be and he/she can tell you what to do.