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Unfortunately what your doctor has said is right. Spotting in early pregnancy is normal. But a fall or no rise beta HCG is a poor sign. Beta hCG is a hormone produced from fetal tissue. At a level of 25 mIU/mL urine test is positive it doubles in 48 hours. So if the result of 7th is 125, then on 9th it should have been around 250 or more. Only healthy fetal tissue can produce an adequate amount of this hormone, so indirectly we get to know the health of the embryo even without seeing it. So it just means the fetal tissue is not growing. There can be lab errors, so to be on a safer side doctor has asked you to come for scan, to confirm.
If you are worried about the repeated miscarriages, have yourself and your partner checked for any problem. Causes like blood sugar levels, thyroid hormone problems, or prolactin hormone abnormalities, any structural problems in the uterus or any problem in semen. Do not lose hope, if you are getting pregnant without much help, no matter what the outcome is, then you will surely have babies. I hope I have clarified your query, do write back if any more questions.