There is a hole. in This is my life

I got everything a 20 year old could possibly want. I have a wonderful husband who would go to the ends of the Earth for me. We just moved into our own home, its nothing fancy, but its ours. I have 2 kids, a 2 year old and am currently pregnant. Everything is going good for us, so why do i feel like there is a hole in my heart, like something is missing. I tired filling it with a dog, i thought maybe a house pet would complete the family, but once we got one its like i wouldn’t even care if she ran away, i don’t know maybe it wasn’t the right dog or was it even a dog i was wanting? I just cant get out of this slum i’ve fallen in. I know he has noticed something is off with me here lately, hes asked multiple times whats wrong but how can i tell him whats bothering me when i myself don’t have a clue whats going on! I cant even write it down cause i don’t know what to say or how to put it into words whats going on. I feel like I’ll never find the answer, this Isn’t the way i thought id feel once everything was going my way.