Why is my boyfriend FIXATED on every physical ailment i have and the possibility of pregnancy?

i have been with this guy for about 5 months. we are very ually active. i got a little yeast infection, and it is the end of the world. he is constantly asking me if i am ok and how i am feeling, and is busy trying to diagnose me with other things like UTIs, as well. i cant complain about feeling nauseous after eating too much or bodily aches and cramping from exercise, or general tiredness, without him telling me it makes him paranoid it i might be pregnant. it is very unlikely i am pregnant,as i am on birth control, and these little symptoms are just things i experience on a daily basis. last night, he was acting so serious, saying he was worried about me, and was clinging to me and hugging me during most of the time we slept. all this, over a yeast infection which has been present for 4 days, and is mostly gone! what makes someone respond like this?