Hello,
Thanks for your query at DoctorSpring.

Let me know your associated symptoms along with mentioned.
Do you have itching in lesion as visible in attached picture?
Does your colleague has similar type of lesion?
Are these elevated red lesions coming regularly at interval or persisting since long time?
do you have some sort of stress?

Let me explain your query one by one.

With the available described symptoms and attached pictures, there could be possibility of urticaria (red large macular lesion visible on abdominal skin) with some psychiatric component.

There could also be possibility of some viral infection acquired from animals while the possibility of Anthrax appears to be least. Anthrax is a life threatening condition with history of death of some animal.

Visible pulsating heart beat is a common phenomenon and more experienced in thin built people
and it should be taken as normal.

Presence of mucus with associated stress (if present) suggests diagnosis of Irritable Bowel syndrome (IBS). Low dose Selective serotonin reuptake inhibitors may help in such conditions.

In my personal opinion, you should go for monogamous sex in spite of multigamous sex. Although you have found to be STDs free but there appears to be high chances of such type of infection.
Throat infection and eye infection (conjunctivitis) could be a part of these disease.

In my personal opinion, Cephalexin won't help in such conditions.

You should consult with internal medicine specialist and should go for thorough check up.

You should also go for complete blood count, IgE, absolute eosinophil count, serology investigations for Epstein Barr virus, Cytomegalo virus, HPV virus, and herpes virus.

Treatment depends on exact diagnosis.
Meanwhile, you should take Cetrizine along with montelukast on written prescription from a local doctor.

Take care,
Hope this helps, please let me know if you have any other queries.
Get well soon,
Dr. Mayank Bhargava