M.V.
About stress...
Stress burns through your vitamin B reserves. If you are deficient on vitamin B's generally your body won't even conceive. The following is a personal inventory you can do to see if vitamin B is the cause or not.
First thing to do is look at your nutrition. How much fiber do you consume? Vitamin B is located in the fiber of foods. Like vitamin C needing bioflavonoids to be best absorbed, vitamin B needs fiber. If you are getting enough vitamin B and fiber then the next thing to look at is how you perceive people. If you frequently see people as enemies, then you are going to be pilfering your vitamin B reserves to keep up with that perspective. The solution is maintaining an internal standard of always seeing others as people, assets and esteeming them as such. There is a book called The Anatomy of Peace by The Arbinger Institute that is genius in transforming our inner perspectives of others. The last thing is to check how your sleep is. Do you get to bed pretty early?
I found it amazing that our liver's job is that of nutritional accountant for our body. It can hold up to a year's supply of vitamins in it and if there are deficiencies, to save our life, it will protect us from trying to build another person (baby) on empty because doing that will threaten not only the baby's life, but our own too.
If everything I mentioned is on track then you might want to look into other reasons for this hold up to baby number 2.