Is it ok for me to be taking a fish oil with d3 added along with a garlic and b12 supplement? im 25 years old, 6'2" and 260lbs.

Yes: These are all perfectly safe and generally beneficial to take. In the fall and winter months adults need about 5000 iu of vit d a day to achieve a good level of vit d, so if your fish oil does not have 5000 iu of d3 (which is unlikely) then i would advise taking additional d3 at that time. If you spend much time in the midday sun in spring & summer that should provide adequate d during that time.