What could be cause of my skin rash after giving birth?

Sorry to hear that your skin rashes are breaking out all over. Sandfly or insect bite reaction is due to a hypersensitivity response of your body to the insect bites. In susceptible individuals, the body mounts a hypersensitive or ‘allergic’ response to the foreign protein deposited in the skin from the bite. The reaction can persist for weeks to months after the initial insect bite. People with atopy (ie asthma, eczema or allergic rhinitis/sinus) may be more susceptible to insect bite reactions.

Your description sounds typical of angular cheilitis, which is a fairly common inflammatory condition affecting the corners of your mouth. It can be caused by several things, eczema being one of them. It could also simply be due to dry, chapped lips. Occasionally, it can be caused by a type of infection due to bacteria, yeast, or virus. Depending on the underlying cause, it may persist indefinitely if you don’t seek help from a doctor. GPs will be able to start you of with the right treatment, and they may refer you to see a dermatologist if necessary.