Claritin (loratadine) d is making me too jittery. Is there an allergy?

Claritin (loratadine) d. This is a side effect of the decongestant in Claritin d. It is not an allergy. You can take plain Claritin and avoid the problem. For your nasal conestion i would try a saline nasal spray and if no help, ask your doctor for a prescription nasal spray.
Claritin-D. Claritin (loratadine)-d is a combination of Loratadine (effective antihistamine) & Pseudoephedrine (decongestant). The former may rarely cause sleepiness while latter can make you feel jittery. This isn't a typical allergy. Just use Claritin (loratadine) alone (not claritin-d) if you need to take something.