Yes, your plantar fasciitis can get worse before it gets better and starts healing. When you feel pain in your heel, at the start of a day, even after resting the whole night and that pain, which doesn't ease out but prolongs the entire day, it means it is getting worse.
If you feel you cannot bear to put pressure in your heels, it means that your plantar fasciitis is not getting better. Also, the pain will start to spread into the arches of your feet, which in turn will affect one foot more than the other, or disperse into the full arch.
When you feel the pain increasing, you will knowingly or unknowingly put pressure on your knees, and you will have worse knee pain as well by the end of the day. Moreover, if you don't take care of the pain, and rest your feet, the problem will move upwards to your hips and lower back, thereby causing severe issues to the whole body system.