My baby is almost 3 months old. I started out breastfeeding but only breastfed for maybe 2 weeks. I want to go back to breastfeeding...?

Relactating. It is not too late to relactate, but it will take some time/effort and patience. You should find out how to set up a supplement system so the baby suckles at your breast and gets formula and the little bit of milk you may be starting to produce a the breast. A tube is taped along your breast with the tip by your nipple and the milk put in a syringe hooked up to it. Seek lactation consultant help.
Maybe... Did you switch to formula, or did you pump and feed breast milk via a bottle? If you switched to formula, you may not be able to restart milk production. You can try, but you might not be able to breastfeed now. If you continued to pump, you have a better chance. Even though your infant has gotten used to the bottle, they probably can switch back to breastfeeding (no guarantees).