Your husband needs his head examined! When did he get his medical degree?? You can both be perfectly healthy & fertile & not fall pregnant, or he could have a low sperm count & you were just lucky once!!!!
You're 23 & if you're this uptight about only having been pregnant once it may be that it's that(being uptight) that's stopping you falling again, especially with a husband who shows such a lack of consideration & knowledge of the real world & how things do & do not happen. What does he think you are a rabbit??
Women can only fall pregnant if the man does his part right (that includes having a reasonable sperm count & him relaxing you) & if they (the woman) relax & stop worrying.
But it seems like the best thing would be for you both (yes him too) go & get checked, although my dr would laugh you out of her surgery, especially if it's not that long since your first child.