I take allegra (fexofenadine) in the morning. my doctor prescribed singular at night. i took it once & had a really severe headache all night. should i take it again? cut in half? or look for something different.

May not be medicine: The headache could be medicine, but could be allergy. Talk with your doctor and try again. I hope you feel well soon.

Not enough info: Sorry, but we don't have enough info to answer your question accurately. You do not say how long you have been on the Singulair (montelukast) or what other meds you are taking, and your other medical history . Please, call your doc's answering and ask if you should try again. You will be able to reach your doc or another one who is covering for the weekend.

Hard to say: As with a single dose and a symptom that is nonspecific like a headache, it could be from the medications(as headaches are a common side effect seen in almost 20% of patient on singulair) but it could be related to so many other things going on with your body/life(including severe allergies) that either another trial or just reviewing this with your prescribing physician is reasonable.