Allergies involve inflammation. All of the tubing in your lungs could be inflamed. That would cause difficulty breathing. I had an uncomfortable feeling in my lungs for a couple of years. No one could find anything wrong with me and suggested I see a shrink. (Well, I wasn't wasting my money on that nonsense.) It finally turned out to be an allergy to oranges. My first allergy. I stopped eating oranges and I was fine.
Hi, welcome to the forum, there are many reasons for congestion in chest. If you are having difficulty in breathing and congestion then may be a asthma. Asthma is an inflammatory disease of the airway and mainly arises from allergies. Hence you have allergy in past few days; there is release of endogenous histamine which causes bronchospasm and breathlessness. Some of the common characteristics or symptoms of asthma are recurrent breathing problems, breathlessness, wheezing, chest tightness, coughing etc.
Some other causes for congestion are inflammation, heart disorders, pleurisy etc. You need to undergo endoscopy and ECG if you are having discomfort. Avoid fried processed food, curd, heavy milk products as they increase mucus secretion, drink warm water, avoid over eating, guava, papaya, banana, steam inhalation etc. You can take antibiotic if infection and broncho dilator may help. I suggest you to consult physician for further evaluation. Take care and regards.