I have had allergic reactions to lavender and I am wondering if lavandin is ok?

Probably not. Lavender oil is from the species lavandula augustifolia (english or common lavender). Lavandin oil is from the hybrid species "lavandula hybrida" which is a cross of lavandula augustiflolia (english or common lavender) and lavandula latifolia (spike lavender) so many of the coonsituents of the oils are the same and can cause the same allergic reaction that you developed with lavender oil.
Not OK if allergic. If you have experience allergic reaction to lavender, you have a chance of allergy to lavandin also as they is related species.