Falling asleep

Please help I’ve tried telling her pediatrician how hard it is to feed her and she didn’t give me any suggestions other than she’s is probably colicky.. Breastfeeding is really hard and I’m finding myself getting really depressed and upset about feeding her as it never seems to just stop. She won’t pull off indicating she’s done feeding so I never know when she’s actually full and I’m feeding all day everyday. She’ll be 12 weeks and I know it’s worse for the leaps but this has been a thing since day one. My baby will fall asleep breastfeeding, and idk how to keep her awake. She falls asleep of reduces sucking and I put her down and then she fusses, usually do this about 4-5 times until she stops and continues sleeping. Is it bad that she keeps doing this? I try to keep her awake but idk what else to do, I’m so tired. I don’t have a chair in her room so I have to resort to standing. She nurses for 30 minutes to sometimes over an hour and it’s exhausting. I know I have to try and put her to bed or a nap when she’s like awake but drowsy and that has only happened maybe once or twice and she’s fallen asleep. I don’t wanna create any bad habits but I also have no idea what the hell to do.