Wieght loss muscle gain qeustion.

Ok so here's the deal.. i am 21 years old i have a 3 year old and an 8 month old i am 5 "4" 123.2 lbs. I have a decent rack (32 g but i'm still nursing so that will go down( no *** and i mean NO *** my waist is 26 inches around my stomach is 30 and my hips (not but the bony part of my hips just below my belly on) is 31 inches around....now you have the visual here's here is the question. I am trying to get down to 108 that 15 lbs... I eat 1800 or less calories a day by body combined with nursing covers that...i start out at zero calories.. I do cardio and "the stepper" for 3 hours a day that depletes 1800 calories then i do strength training abbs obliques upper body all that for another hour or two...Logically i should loose a pound every other day right? NO i gain 3 pounds lost it in about 4 days then woke up to day and gained 2 freaking pounds!! WTF how did again weight if any one knows please i'd love to hear it. PS> just so every one knows when i work out my kids are playing right next to me and if they need me i stop help them and then add 10 minutes to my work out...they never cry more then twice if i have to stop i do...theydon'te mind at all and i take sunday off to spend with them, myhusbandddoesn'tt mind either because i'm getting a body he's never seenbe forr (i'm 20 lbs less then when we met)