Welcome to HCM
There is nothing to worry. The dent is pretty normal, due to development impressions are formed on skull and the dent is probably that. So nothing to worry. Regarding the allergy
in not and blocked nose please take steam 2-3 times a day, do warm saline gargles and you can take OTC antiallergic drugs to get symptomatic relief. Don't think about the dent again and again as it is a normal incidental finding.