My sunburn feels like it did something to my muscles?

I laid on the beach for the first time in 15 years yesterday. I used SPF 70, but I am very pale and it didn't work great. I am burned on my back and the back of my legs. It feels like my muscles/nerves hurt when I walk. Is this a bad sign? Sign of a degree burn?
My sunburn feels like it did something to my muscles?
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