OP, with respect, you come across as being more concerned about how you can have time off rather than focusing on how to demonstrate your commitment, maturity, and personal responsibility - which is what your employer will want to see.
Your focus needs to be on minimising absence and in terms of any medical condition, you need to demonstrate that you are taking responsibility for it; ie working with your GP to find a solution to your heavy, painful periods. IF your employer doesn't terminate your employment, then the best thing you can do is demonstrate the above; if they do- then you will want to be able to demonstrate it to a new employer.
I understand heavy painful periods - I had them myself for years; turned out I had major fibroids and ended up having surgery - but I at least could prove to my employer that I was dealing with the issue. I rarely took time off anyway for my periods - only towards the end when I was being lined up for surgery as the situation was getting very very bad. Once I had my surgery I was back to work and fully committed. I'm still there 10 years later and doing well. I am rarely off sick.
Your iron tablets aren't solving the problem - they are dealing with the symptom of fainting (not very well by the sounds of it) - you need to find out why your periods are so heavy and painful - and look into ways to resolve it - ask for a referral to gynae or whatever you need to do. It shows you are taking personal responsibility.
Re a cold/flu - I'm someone who believes if you are sick you are sick; however, that said, you need to learn some resilience and how to dose yourself up and push through - everyone has to do it sometimes. If nothing else it means that if you are genuinely REALLY sick and can't avoid time off, your employer will be more understanding because they won't see it as taking the piss. If you are off all the time then it becomes tedious and you end up with no credibility. It affects your reputation in the company and, assuming you keep your job, you certainly won't be considered for promotions, opportunities etc... as your conduct shows you don't take your job or the company seriously.
With the greatest of respect - you need to grow up. Demonstrate that you take responsibility for your personal health and attendance. Acknowledge where you have failed to live up to your employer's expectations and if they are good enough to keep you on - go ALL OUT to PROVE yourself ie. no more sick days and see your doctor to get your periods sorted properly.