I understand you, with side effects like that, it's less tempting to go to those molecules. Some molecules may be less worse than others for weight gain and other side effects. On the other hand, natural products are less recommended, not because they are ineffective, but because their effects are less predictable and they have many interactions with drugs.
Effectively, Celexa can make you gain between 10 and 30 lbs on average. Most first generation molecules like Celexa have this effect (the worst being Paxil). More recent molecules, such as Trintellix, Fetzima have a more neutral effect on weight. However, they are more expensive and are only reimbursed by private insurers (not reimbursed by RAMQ).
Wellbutrin can help with weight loss, but since it can increase anxiety (it's used more for depressive disorders), it's not a good choice for you (you've already tried it anyway)
In your situation, my opinion (again this will have to be decided with the doctor) is that Prozac might be a good choice for you. It is reimbursed and, despite being a first generation agent, it has the least effect on weight.
As a second, Zoloft would also be a good choice. It controls anxiety very well and is generally very well tolerated in terms of side effects. The effect on weight is variable from person to person, but the majority of my patients do not gain much weight on Zoloft.
The third one that could be tried is Cipralex. It also plays a little less on weight, is relatively well tolerated. I put it on par with Pristiq as well.
Two other molecules that are effective for anxiety and are not in the same family as antidepressants are Remeron and Seroquel. However, I would not suggest them to you they make you gain even more weight than antidepressants (despite being very effective for anxiety symptoms.
I hope this review of the different molecules can enlighten you on the choice. Before I finish, I would like to mention that with the information you have given me, it is crucial that you have a treatment that is effective, well tolerated, affordable and improves your quality of life. When you find the right molecule, you're going to be fine. That's what every patient who is well controlled tells me.