Many thanks for your query and the coherentt deatails.
What you have described, apperas to be ACUTE URTICARIA
It is type of an ALLERGIC reaction
The causes can be many and varied. Eating out (specially- 'chinese food', seafood, nuts, chocolates etc ) is a common cause. Temperature changes, exposure to dusty environment, intake of medicines, common colds, viral infections are also very common causes of such conditions.
The headache and the 'heartbeat-feel' does not appear to be related or significant but could be linked to a viral prodrome- impending viral infection.
Will need certain more details before a medicine can be prescribed