When I’m walking from my knee to my shins becomes very heavy. Is this one of the signs in fibromyalgia?

It wouldn't be a symptom generally associated with fibromyalgia.

You may instead simply have some temporary strain upon the knee which is slow to resolve because walking is so demanding upon the knees.

Please be sure to avoid using heeled shoes for a while and try applying some Atrogel^® to the area morning and evening.

Apply a bag of frozen peas if it really flares up.

It should improve within  a few days or weeks, depending upon how much you are able to rest it.

Best wishes

Earle