Severe cough, breathless, feel hot. Tried allegra, benadryl, dietary changes. Diagnosis, solution?

Since the last five years the current season i.e. the beginning of summer till the rains come, I have suffered from coughing. This coughing can be severe enough to keep me from getting sound sleep in the night. Sometimes, I also get breathless and feel extremely hot, even in AC. I have been coping with this problem through various ways.
1. I have changed my diet to include a lot of roughage, no chillies, oil, and proteins. I have also reduced the amount of food I take but increased the frequency.
2. I have tried allegra in seasons past but it was only mildly helpful.
3. Last two seasons, I have focused on using benadryl which gives me considerable relief. Dosage: two spoons every four hours. In especially troubled moments I top this with an extra spoon. It seems to help.
4. I am slightly overweight at around 70-75 with a height of 5'10 1/2''.

Would greatly appreciate your help in terms of diagnosis and solution.