Constipation, gas, and heartburn

The constipation is bad!! I then feel gas is trapped and then the heartburn begins. I have been taking 2 tums around supper time but that is all. What can I do😫?? I am eating plenty of fiber AND drinking a gallon of water a day, nothing is helping. And not to mention, when I did finally “go”, I had red blood in my stool and because it was so hard, it hurt so bad! Need advice!! This feeling is rough!! I’m 15 weeks!