The lip swelling may be due to various causes like trauma, allergy, insect bites, organ failure, cheilitis, bacterial or viral infection, fluid retention etc.
You should have the relevant investigations done like bleeding time, clotting time, pt/inr, cbc, serum urea, creatinine, liver function test etc to know the underlying etiology.
The drugs like lexapro may also cause thrombocytopenia and increased risk of bleeding and in that case the change in drug may be required if the symptoms are severe.
The allergy to food, drug or insect bite may also such lip swelling and antiallergy drugs like benadryl is helpful in such symptoms.
The treatment depends on the underlying cause.The other causes should also be ruled out.
Here is the link for more information
side effect of lexaprocauses of lip swelling
Let me know if you have any doubt.