This sleep thing...

Is it normal for a 14 month old to STILL be inconsistent with his sleep at night? He was sleep trained at 5 months and by 8 months was going to bed on his own and sleeping all the way through with no issues. I went back to work 3 months ago and since then it’s been so inconsistent. I started rocking every now and again and sometimes that doesn’t even work. Some nights he’ll go to sleep on his own and sleep all the way through. Other nights he’ll scream and cry and I’ll have to rock him. Sometimes he’s up an hour after I put him down, sometimes 5 hours later. What the hell is going on? Last night he was up from 12-3 and WOULD NOT go to sleep no matter what I tried. I’m having another baby in 3 months and need to have this figured out by then! Hoping it’s just some sort of regression and will work itself out.