We are sorry to hear of the difficulties you are experiencing.
While it may be possible that excessive straining can cause vaginal/cervical bleeding, unless you can have a doctor or bodeket taharah confirm the source of the blood, you may not attribute this blood to dam makkah, and should assume it is dam niddah.
However, given your circumstances, you may reduce the number of bedikot required to one per day during the seven clean days to avoid the problematic afternoon bedikot. We hope this will help you immerse in a timely manner. If you still experience difficulties completing the clean days, we recommend consulting with your doctor to try to find the source of the bleeding and get back in touch with us for further instructions.
Please feel free to get back to us with any further questions.
B'hatzlacha!