What Causes Severe Cramps And Frequent Urination After Having Sex During Ovulation?

We have been trying from last 6 months. Every month I feel stomach cramps and urination started before period due date. We do keep track of ovulation time and have sex during the week. Every month due to stomach cramps, urination I feel I get pregnant but period occurred. My question is, in both the below cases I do not get pregnant but why do I have pregnancy severe symptoms before a week from due date of next period. And urination is severe enough that I go to washroom every 15 mins. Scenario1: We did not have sex during ovulation and I am having no stomach pain, urination before period next date. Obviously I am not pregnant. Scenario2: We have sex during ovulation. We verified egg size also. I had severe stomach cramps and urination started before a week from next due date. When I tested , It results negative. Its OK I am not pregnant in both cases but Why do I have severe cramps and urination every time we do sex during ovulation. FYI, I had 3 miss carriages earlier. Thanks and Regards