<s>[INST] My blood pressure today is 108 over 72 and pulse rate 84. I was prescribed Vibrox Capsules 100mg (Doxycycline) for sinusitis and started taking the medication 3 days ago.  After taking the first 2 capsules together (the dose prescribes for first day) I felt sick, weak and fatigued. I read that this medication can cause low blood pressure. Are the side effects I am experiencing what I should expect whilst on this medication? [/INST] Hello and Welcome to ‘Ask A Doctor’ service.I have reviewed your query and here is my advice.Doxycycline causes nausea and diarrhea. So, your symptoms are pretty normal.If you experience any other symptoms other than these, please immediately consult your general physician.Hope I have answered your query. Let me know if I can assist you further.Regards,Dr. Muhammad Adnan Iqbal </s>