Allergies such as hay fever can continue or even worsen during pregnancy, and managing symptoms matters for comfort and sleep. Several antihistamines have been used widely in pregnancy and are generally regarded as suitable, but the choice depends on how many weeks pregnant you are, whether you are breastfeeding, and your individual circumstances, so this is a decision to make with a professional rather than from general information.
Non-medicine measures are a good first step in pregnancy, including avoiding known triggers, keeping windows shut during high pollen counts, using saline nasal rinses, and applying a barrier balm around the nostrils. Steroid nasal sprays and some eye drops may also be options your doctor can advise on.
Before taking any allergy medicine while pregnant or breastfeeding, check with a doctor or pharmacist so they can recommend the safest suitable option and dose for your situation. Do not stop essential medicines, such as asthma treatment, without advice, because uncontrolled asthma carries its own risks in pregnancy. Seek urgent care for any severe allergic reaction at any stage of pregnancy.