Could My Back Pain After Taking The First Dose Of Losartan Be A Side Effect, And Should I Skip The Next Dose?

I have high blood pressure and I've had it for at least 30 years. I am 64 now and I'd been taking Valsatran and doing ok. My doctor changed my med to Losartan 100mg since I took the first dose today and now I'm having a pain in my back like a muscle is tightening. What's up! I will not take another dose until i reach her,