in fishman area it’s been like 30 days since pregnancy so i changed difficulty down and not able to have child still

it is snapshotted at conception reducing difficulty doesn't speed it up also keep in mind it used to be longer across the board was 74+ days

Pregnancy time is perfect length. Lategame, it takes something around 3 days or so. Raise SB Womb level to 10; trading with Goblins is probably the most direct means of doing this, and you can search up SB Womb (Seedbed Womb) status up for the details on that. You can achieve max level for this early-game fairly easily.

More than likely, you're not complaining about pregnancy time being too long, though. You're consuming drugs and suffering considerable stamina drain, damaging the baby, preventing it from surviving. Early-pregnancy, it can be difficult to deduce the health of the baby, but generally speaking, you can search these details up if you want the specifics. In short, eating drugs, being hit, using stamina, this harms it, causing the pregnancy to restart before it progresses. Rest when pregnant at the fishman place, and ignore your jobs - as long as they recognize your condition, they'll just decide punishing you would hurt their baby, so they don't.

There's a safe drug on the table to the left that can help recovering the baby. Avoid the aphrodisiac drug to avoid harming it (and drinking any potions, because that harms it, including healing potions, which sometimes took me off guard at times). The first pregnancy may seem long, but it's a sort of 'bad-end' for a reason. I managed to do it all without any guide on my first playthrough, so I understand your point, but as long as you overcome it carefully, you can escape and improve your SB Womb level so it's not a problem later.

If you're not playing on the easiest difficulty, I'd recommend you carefully review the status I mentioned here, since its lactation alteration could come as an undesired surprise if not.