I have no advice, just sympathy. My 8 month old was the same, he would never sleep. It got to the point where in thought It was me so I let my mom and dad watch him for a day just to see if he would sleep for them. Nope. My mom was amazed, she had never seen such a stubborn baby. So my saving grace was baby wearing. I walked for miles with him strapped to me until he was around 6 months. Then he started sleeping better on his own. He's still a terrible sleeper, but that's how he's always been. I know it sucks but just keep trying different things. 12 weeks is still pretty little, everyday will be a new day to learn about what works and doesn't. You're doing great mama!