baby doesnt gain weight and gets constipation

Hello! My 11 mo has stopped gaining weight since 6 months, 7 kg always now, or 7.1. But height is growing. Overall she is very active and happy every day, nothing seems to bother her, she loves eating, she eats herself everything I put in her plate (what she doesn't like she throws away). So her weight is my big concern but also since we've started solids at 6 months she always has constipation problems, never had straight week of everyday pooping, always couple days gaps or even week gap. And then I give her laxatives. So at the beginning I was told to decrease the solids and always stick to breastfeeding, and do not worry about weight. But stool never becomes frequent, and neither weight is growing. And recently I was told by other doctor to increase her solids up to 4-5 meals/snacks per day, because we need to gain weight. So I'm really confused now about our problem. Skinny baby who loves my breastmilk and also loves to eat food. I would love to stuff her belly to make her fat ,but then she can get constipated easily. Like a dead end for me. Please if anyone had slightly similar situation, can you recommend me what to do. I give her many fibers every day, always give her water. We've checked her hemoglobin and it was average normal.