I hope that you are doing well during this time; and that this message finds you in a good place.
I don't want to offer medical advice, but I will help to try to explain a few processes that may be contributing to the feeling that you are describing. However, if you are experiencing pain; you may want to consult your doctor.
Firstly, scientists have shown that the feeling of falling in love often triggers a sympathetic nervous system response. This means that it triggers a release of a cocktail of hormones, including acetylcholine, epinephrin, and norepinephrine. Depending on the context, this mix of hormones being released can be understood as fear, excitement, nervousness, anxiety, etc. by the individual encountering them. This physiological response often leads to constriction of particular blood vessels, and shunting of blood to areas of the body that might require it for quick escape, a survival mechanism that has been evolutionarily conserved. That being said, blood is often directed away from the digestive system, including intestines and stomach. If blood flow is restricted from this area for a prolonged period of time, you may begin to feel queasy, and perhaps some pain.
Secondly, scientists have linked the feeling of falling in love with activation in brain areas responsible for pain perception, including the anterior cingulate cortex, thalamus, and insula. Depending on the person, the combination of the changes in restricted blood flow, and involvement of the "pain matrix" in the brain, may cause someone to interpret some of these changes from peripheral neurons firing back to the central nervous system, as painful experiences.
Lastly, it may not be unreasonable to think that with the release of a cocktail of hormones, and constricting of particular blood vessels, that the blood vessels in the uterus experience increase blood flow to the cervix and uterus. This may trigger prostaglandin release and uterine contraction similar to that which one might experience when having their period.
I hope that this was helpful. Feel free to reach out if you have anymore questions about human physiology, biology, and neuroscience!