Miscarriage

Pretty sure I'm having a miscarriage. I found out I was pregnant at 3 weeks and 1 day. Everything seemed like it was going well so far. I am 5 weeks today and started cramping. I didn't think much of it because I know cramps are normal. Then I had some light pink spotting only when I went to the restroom. That lasted a few hours and then started increasing in flow. Now by this evening I have heavy bleeding and a large clot. I'm so heartbroken. I have a dr appointment tomorrow but feel like it's pointless now. I haven't told my hubby that we were expecting yet because he's traveling for work and I wanted to tell him in person. I was so excited to surprise him. How does this happen? I don't understand how and why some pregnancies last and others don't. I mean I get the physics of it but I emotionally don't understand why this happens. Sending lots of well wishes to all you ladies and hoping someday soon I can join back in this group