On amoxicillin for chest infection . day 2 on antibiotics developed bad headache . day three still present and making me have nausea is this common in this antibiotic ? five weeks pregnant .no fever present but paracetomol not helping?

Stay well hydrated, monitor temperature and breathing. A flu vaccine is recommended, unless otherwise contraindicated. Your symptoms may be viral if the antibiotic is not improving your chest infection. Headaches may have a number of causes and high blood pressure should be ruled out. Watch for signs of breathing difficulty. Please follow up with your physician.

Most chest infections are due to virus and not a bacteria so antibiotics will not help. Or perhaps you have COVID if not vaccinated. Get tested.