Any advice on what to do!!!

I have a three year daughter from a pervious relantionship. We decided that she'll go visit her dad one weekend and the next weekend I'll have her and what not but I dont know what to do, when my child is over there she acts like if I mistreat her and she saids that she doesnt want to come back with me but when she is over here she acts totally different and just to put things out there I dont mistreat my child of course she got to have dicipline but I guess when she is with her dad, he lets her dowhatever she wants to...for example I told him she cannot eat candy but when I open her bookbag its full of candy, he lets her stay up late knowing that she is going to start headstart soon, he lies and saids that he took off of work in order to be with her but I know it is lies becuase he would never take off a day of work but aneways he lies and saids that he with her but really his 16 year old sister is taking care of her and all that little girl do is smoke weed and be with her boyfriend showing her bad examples.....and everything that I know is because someone else tells me which I trust and she keeps me posted in how my child acts when she is over there..but I seriously don't know what to do...I love my child so much...but she is picking up after her fathers bad habits...and Im pregnant with my second child and its just too much stress on me Im loosing my mind.......any advice??

STOP SENDING HER OVER THERE GET FULL COSTODY