Penicillin and its derivatives have been around longest, and are therefore the least expensive and most widely available. The more people take them, and the more frequently the same person takes them, the more opportunities there are to develop an allergy.

No.

There are some health conditions that can cause abnormal or irregular periods and also affect fertility. For example, PCOS and hypothyroidism can cause heavy periods and make it harder to conceive, or increase the risk of miscarriage. Endometriosis can cause heavy periods and increase the risk of complications in pregnancy.

But there is no known connection between the rate of flow in normal periods, and the intensity of pregnancy symptoms.