I'm new

Ghewa
Hello all. This is my first pregnancy and I am in my sixth week. I have 2 questions please:
1-  I spotted brown spots on my panties yesterday, went to the doctor and had a blood test. They told me that everything is fine, but I still have pain in my back and I felt some pain in my stomach during night. Is this normal? Is there anything I should worry about?
2- My first blood test gave a value of 88,5 mII/mL and that's when I know I am pregnant, 2 days later the test showed 251,2 mUI/mL. And the dr asked me to repeat the test after 2 weeks and she said that the result should be 1500 mUI/mL. Yesterday my results showed 29.587 mUI/mL. My husband and I were wondering if this means that I might have a twins because the result is almost the double. Is this correct or everything is normal for a single fetus. Thank you in advance :)