the trinity why 3 Gods or 3 persons Mark 12:29 1 Corinthians 8:6

why does the doctrine of the Trinity seem incomplete or misleading , as though we can take verses from the bible and construct our dogma to explain the unexplainable . Can God be explained in another way by adding to the doctrine , or by perhaps praying and getting Gods input to create a better doctrine?---remember the trinity doctrine came out after the bible was completed , and derives conclusions beyond the intentions of the original authors and the Holy Spirit . It was formulated way after the apostles and early church fathers ----who by the way were mixed in their conclusions , they seemed to favor tertullian's conclusions , but still it is a extra biblical doctrine , or dogma, in my opinion.