Do I Have the Holy Spirit?

I was reading in Acts today and the thought struck me, do we receive the Holy Spirit upon belief in Jesus Christ? Is that something truly founded in scripture? the Apostles believed and hid in an upper room, believed and waited before the Holy Spirit descended upon them. It never says that the Holy Spirit descended upon the Eunuch. Never does it say that people were baptized in the name of anyone but Jesus. The gift of the Holy Spirit was just that, a gift given by God to provide power in the witness and boldness and comfort. Where did we get the assumption that we could baptize in the name of the Father and the Son AND the HOLY SPIRIT? What gave us the right to assume that we could tell someone they automatically received that gift? I pray that we would be careful with the gifts of God, that we would hold them as precious as diamonds and fragile as a spider web first thing in the morning. That we would remember to not add to or take from scripture in our arrogance or zeal. And to pray, for humility discernment and knowledge.