32 weeks pregnant with flu. Doctor prescribed nasonex (mometasone) but it is not working. Can I take dristan instead? It has always worked really well for me.

Both not the best. Nasonex (mometasone) (corticosteroids) has been assigned to pregnancy category c by the fda. Dristan (ibuprofen/pseudoephedrine) has not been formally assigned to a pregnancy category. Animal studies failed to reveal evidence of harm. Use in late pregnancy leads to premature fetal PDA closure. The recommendations are during pregnancy use, when there are no alternatives and benefit outweighs the risks.
Ask your Gyn person. Although it is unlikely that dristan would have a detrimental effect on your fetus, it is medico-legally wise to only take advice from your ob-gyn doctor.