Brittany, we don't call this Hell Week for nothing. Everything you are experiencing is perfectly normal...and it will get better. Quitting is a a roller coaster, big highs followed by big lows, with some medium stuff in between. The breathing is normal, too. Try taking voluntary deep breaths, I found this article:
Anxiety Breathing Techniques
Four-Seven-Eight Breath
Best done sitting but can be done standing or lying down.
1. Sit with your back straight and your hands resting comfortably in your lap or on your thighs.
Look ahead...try not to fix your gaze on anything in particular. Slightly closing your eyes helps.
Try to focus internally on your breathing.
All inhalations are done through your NOSE; all exhalations through your MOUTH.
2. Commence inhaling slowly, smoothly and deeply to a mental count of 4 seconds. Fill your lower lungs first (by pushing out your abdomen), then your middle and upper lungs.
Hold your breath for a mental count of 7 seconds.
Slowly and smoothly exhale for a mental count of 8 seconds.
As you exhale, try to let go of all your anxiety, tension & stress.
That's one round. Pause briefly without inhaling then start another round. This natural pauseis very therapeutic and relaxing.
Do 10-12 rounds to begin. Build up to 25-30 rounds several times a day AND whenever you feel anxious or nervous, etc.
Summary: Inhale for 4 seconds - Hold for 7 seconds - Exhale for 8 seconds - Pause briefly - Repeat.
Benefits
Calms your mind
Tones your nervous system
Regulates your breathing
Balances your emotions
Tips
Can be done anywhere - on a bus, in a line, at work, before a test
If you lose your breath, stop, breathe freely then try again
With practice your pauses between rounds will naturally get longer
Soothing music or ear plugs can help reduce external distractions