I think noe you should only focus on baby because as you said your baby is 3 months old so he needs breastfeeding and it is very important for baby growth and for proper breast feeding you can use hug-a-bub baby carrier. For more details visit http://www.hugabub.com/flex/the-hugabub-traditional-ring-sling/167/1.
It took time to put it in and it takes time for it to come off. My daughter is 2.5 months old and I still have 17lbs to come off (put on 42). I was doing good walking or going to the gym till I went back to work three weeks ago. Now I only have two hours in the evening with her. That time is precious so I'm only working out on the weekends now. If you are nursing you can't diet but you can eat healthy, wholesome food. In a year you'll have more time for workouts. Right now love and bond with that precious baby. Believe me, I HATE wearing jeans that are two sizes bigger or having a giant muffin top but not a much as I would hate to miss the smiles and cooing that will be gone too soon.