Had a miscarriage. Still need to take prenatals for 6 weeks. Throat is dry and I think its from my seasonal allergies. Can I take Claritin (loratadine) or zirtec?

Zyrt/Clar ok to use. You can use Claritin (loratadine) or zyrtec (antihistamine) however a dry throat may not necessarily be a symtom of allergies. Antihistamine and other medications can cause further dryness. Make sure you keep hydrated after miscarriage as you would have had significant blood loss. Salt water rinses sometimes can soothe a sore or irritated throat.
Yes. Either Claritin (loratadine) or zyrtec is safe to take with pre-natal vitamins. Zyrtec may cause drowsiness; so be careful with driving or operating machinery. Gargling with warm salt water may help with the throat dryness as will sucking on lemon drops (sugar-free if you're diabetic).