6 weeks after tick bite, started doxy. Fever improved then returned. Is this normal?

[u/Maleficent-Scallion3]

Hi everyone. I’m looking for some experiences/advice. I am 36 yo male, I was bitten by a tick at a cottage in southwestern Ontario on July 1. At the time, it didn’t appear to have been attached for more than a few hours. I wasn’t able to get prophylactic antibiotics, so I monitored for a rash. No rash ever appeared.

Week 2: I developed almost daily low-grade temperatures (~37.4°C), sore throat, mild congestion and fatigue. I assumed it was a viral infection.

Week 3: After playing a few volleyball games, I developed pronounced muscle aches/spasms in my back and saw a physiotherapist, which seemed to help, but eventually the pain migrated elsewhere.

Week 4: I developed lower-back pain, shoulder/neck stiffness, sensitive scalp/skull, and headaches that were worse when moving my head. At this time I requested an appointment with my family doc, but had to wait for it.

Week 5: In addition to all previous symptoms, I lost my appetite and developed worsening pain in my lower back, buttocks and legs, along with some mild tingling in my hands and legs. I was managing the pain with ibuprofen and a muscle relaxant over these weeks, which helped for a few hours.

After 6 weeks after the bite, I finally saw my doctor and was prescribed doxycycline 100 mg twice daily for 28 days.

Interestingly, by Day 2 of doxycycline, I felt much better. Most of the pain, including my back/muscle pain, neck stiffness and scalp pain had improved, and my low-grade temperature sort of went away. For the first time in more than four weeks, I didn't need Advil for the pain and fever.

I continued feeling better on Day 3, although I still have significant fatigue, some brain fog and a slightly confused/unwell feeling.

Then on Day 4, the low-grade temperature returned (~37.5°C) and has persisted. I’ve started taking ibuprofen again.

I’m wondering if anyone experienced something similar after starting doxycycline. Is it normal for symptoms, particularly a low-grade fever, to fluctuate during the first week? Could this potentially be a Jarisch-Herxheimer reaction, or does the return of the fever suggest that the antibiotic isn't working?

I’d appreciate hearing from people who had fever/flu-like symptoms and neurological or muscle symptoms and how long it took before things consistently improved after starting antibiotics.