I have backpain on right side. similar to a light muscle spasms. woke up this morning with rash (on right side) with small blisters. it is not itchy, but the area seems painfull?

What you described is suggestive of Shingles. If the rash is limited to one side of the body, it is very likely to be shingles. See a doctor as antiviral treatment may help in limiting the extent and severity of the lesions. Your doctor may also provide pain relief. Visit this site for info: https://www.mayoclinic.org/diseases-conditions/shingles/symptoms-causes/syc-20353054 Wish you good health!

I too believe you have contracted an outbreak of herpes zoster, causing focal shingles. Should start treatment ASAP to shorten the course and prevent post-herpetic neuralgia. Also prudent to survey potential underlying conditions which might have created vulnerability.