Spirulina is a very healthy food that is high in protein, anti-oxidants and fiber but the protein content in 1-3 grams of spirulina is negligible. Just think about it realistically. What is 2g of protein going to do? That's like taking 1/15th of a scoop of protein powder after your workout.
Keep taking the spirulina but use it as a greens supplement. It doesn't replace the need for a protein supplement.
If you are experiencing stomach issues from protein powder, I suspect you are using a whey protein concentrate. The lactose in the product is what is causing your stomach distress. I would switch to a pure whey isolate.
A lot of adult humans are sensitive to lactose, which is the sugar naturally occurring in milk products. You are going to want to supplement with a pure whey isolate. A pure whey isolate will have no lactose per sugar. A whey protein concentrate on the other hand will have a few grams of lactose per serving. Enough to cause the stomach distress.
Read the ingredients list and purchase a whey protein supplement that contains whey protein isolate, natural flavours, a natural calorie free sweetener like stevia and nothing else.