God does bless us when we give to support His work–but not necessarily by giving us more money. His blessings come to us in many ways, including the joy of knowing that He is using our gifts to help others and point them to Christ.
God doesn't promise to bless us, however, if our motives are selfish or we are giving only because we hope to get something in return. One of the most sobering stories in the Bible is that of Ananias, who with his wife sold some property to give money to the church. (You can read about them in Acts 5:1-11.) But they were only doing it to impress people, and they lied and held some of it back. God severely judged them as a result.
Remember that Jesus–the divine Son of God who left heaven's glory for the sin and corruption of this world–was born into a very poor family, and was poor Himself. On one occasion, He declared, "Foxes have holes and birds of the air have nests, but the Son of Man has no place to lay his head" (Matthew 8:20). While some people of wealth supported Jesus' ministry, none of the apostles were wealthy, nor did they gain wealth by their ministry.
Make sure Christ is first in your life. Then ask Him to help you gain control of your finances by budgeting your income and cutting down on your expenses. Then be generous in your giving, so God's work can advance.