Depending on how long you were smoking you could have some troubles with pain and breathing with your lungs alone. After you quit smoking, it can take 6-8 weeks to feel better and get over the side effects and addiction, again depending on how much and how long you were smoking. It can have caused limited lung volume resulting in your shortness of breath. Withdrawal from nicotine can cause you to shake and have shortness of breath because it has learned to depend on it. So this is normal for a while...

Anxiety also causes shortness of breath. Since smoking reduces anxiety (nicotine) you may not have noticed how much anxiety you actually had. Now that you have removed your source of consolation, you are noticing these effects of your anxiety.

Try to find some legitimate source of relaxation that will help you breathe more easily. Take small time outs from stressful situations to clear your mind and take control of your body's reflexes of anxiety.

It is important that you continue to get the toxins from smoking out of your lungs and system by deep breathing.