Hello and Welcome to ‘Ask A Doctor’ service. 
I have reviewed your query and here is my advice. 
Well if it occurs exclusively when you lay down  then first of all you need to get checked for bed bugs. 
You should  put your bedding  and mattresses 
In sunlight regularly for a few days. 
Change the bed sheets and  pillow covers. 
In case if  there is no improvement  first of all get an 
allergy test done to rule out the exact cause of allergy. 
Avoiding  exposure to the allergen  whether  it is any food or other things  should be done. 
If there is an allergy  outbreak  then you can take anti allergic medicine. 
Also discuss  with your doctor about 
Immunotherapy  of nothing else improve  tge symptoms.. 
Hope I have answered your query. Let me know if I can assist you further. 
Regards, 
Dr. Honey Arora