There is one easy test get some Epsom Salts (magnesium sulfate) put 2-3 tsp in a glass of water and drink it. When the pain goes away in about 20 minutes you will know it is your gallbladder. You can repeat this drink.
Just disolve the granulars in little bit of warm water first.
I get that stomach tightness and ache too, but my pain runs around my shoulders, collarbone etc.