NO! STOP NOW! Combining Phentermine and another sri called Fenfluramine led to the so-called fen-phen crisis in the 90's when 1, 000's developed pulmonary hypertension, a non-reversible, often fatal, debilitating condition. We discovered this because the fen-phen craze created a huge study population. There's no reason to think another sri (celexa) won't interact the same way. Wanna be the cel-phen guinea pig?
Healthy. If you can tolerate some irritability & nausea, you are fine.
Polypharmacy? Diet drugs, while they work, only provide a relatively small benefit that only lasts as long as you take them, and insurance does not pay for them. Chantix has some very serious side effects, including suicide, so i would stay away (use the more traditional patches, sprays, and pills). Celexa (citalopram) is a good drug for depression and anxiety, but can have side effects. Of these 3, this is the best choice.