Yes, it is good to get tested for STD's, but also keep in mind that your WBC count did not drop below 4 until after you started taking antibiotics for Lyme (which suggests it is a side-effect of the antibiotic and/or a die-off or herx reaction to killing the spirochetes that cause Lyme Disease), and the EM rash is a hallmark symptom of Lyme and no other condition that I know of has this as a symptom.
As for the health anxiety, there are things you can do to help yourself with this. I think it would be good to consider working with a counselor who can teach you some anxiety reduction exercises - this will help you with stress reduction and with your recovery from Lyme. A book I used to help with anxiety myself was "The Feeling Good Handbook" by David D. Burns. Another idea is to check out the anxiety forum here at HealingWell, too. And remember, anxiety is a symptom of Lyme and some other co-infections, so treatment of the Lyme/coinfections will probably help too.
Your body needs nutrition and calories to heal, so if food is hard to stomach, maybe a liquid meal replacement mix would help? I used Ensure for a few years to help supplement my diet since I have so many food allergies/intolerances. Others like Carnation Instant Breakfast, Boost, even Slim Fast can be a good supplement.
I hope this is helpful - take care,
Chronic Lyme Disease, Gluten & Sulfite Sensitivity, Many Food/Inhalant/Medication/Chemical Allergies & Intolerances, Asthma, Gut issues (dysmotility, non-specific inflammation), UCTD ("Secondary Lupus-Like Syndrome"), Osteoporosis, Pancytopenia, chronic malabsorption/malnutrition, etc.; G-Tube; Currently TPN-dependent.
Meds: Zofran, Pulmicort, IV Ceftazidime, Heparin (to flush PICC line), Claritin, Colloidal Silver (used topically), probiotics, homeopathy.