I oil and perform minor repairs on my own machines so I've seen the GUTS!
. If you were to open your machine (not suggesting it), you would see that the tension disks relax when the presser foot is up and they apply more tension when the presser foot is down. More tension when the presser foot is down is normal.
You haven't said if you're using different thread, different needles, or a different batting. If any of those have changed it can cause thread breakage.
You haven't said if you've experimented with changing the tension knob. Adjust it down in half-number adjustments until you start seeing thread on the bottom and then step it back.
Also, I'd say that about 90% of the time my own thread breakage is due to the needle. The needle was blunted, had a burr, or was the wrong size. The eye size needs to be large enough to feed your thread and work properly with your batting, so consider using a larger-eyed needle. I would also consider changing the needle, even if you just changed the needle.
Do all of this, even if you think nothing is different than usual. Sometimes you just work with a certain mix of thread, needle, batting that require adjustments to your system.