Hi,
Doxepin is in a class of medications called tricyclic antidepressants and may cause side effects such as nausea, drowsiness, weakness or tiredness, nightmares, dry mouth, constipation, blurred vision. (ref:http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a682390.html)
On the other hand, singulair is a medicine called a leukotriene receptor antagonist and prescribed for the treatment of asthma and allergic rhinitis:The most common side effects include: stomach pain, heartburn, stuffy nose, flu, dizziness, headache or rash. (ref:http://www.singulair.com/montelukast_sodium/singulair/consumer/allergies/for_parents/product_information/ppi/what_is_singulair.jsp)
Your rash may be a side effect of the medications you are taking. Did the rash appear after being prescribed with these drugs? It is best to discuss your symptoms with your doctor and if this is the case, these drugs should be stopped and alternative medications may be given.
Take care and keep us posted.
I have been this route, nothing works but you can make your self sick trying all the powerful stuff they want to give you, Iam trying a Histimine Free diet at presant and taking no prescribed or OTC drugs, I have come to the conclusion it will take its caurse,I have noticed it changes at times and I have been having Dermagraphism where a red itchy streak appears and leaves with a few minutes also big wheals and the Small spots you describe,all htis came on after Dental work done Mid May.