Mirtazapine withdrawal? Or am I bi-polar?

Hi I just feel like I really need to vent and feel like someone understands, I have slowly been weaning off mirtazapine and my last dose was a few days ago and I'm about to start taking fluoxetine as the mirtazapine was making me gain a lot of weight and making me feel groggy a lot, but since stopping I haven't been sleeping great and I've been getting this horrible depressed feeling, it's such a hard feeling to describe it's like such a lonely feeling you feel like nobody could possibly understand:weep: like a sinking stomach feeling and you just want to cry almost like grieving but you don't know what for, it makes me feel like I'm bi-polar or something as it makes me feel erratic and I just had to go sit in the bathroom and sob, it almost makes me want to vomit because it feels so bad! I have had feelings like this before as I have suffered from anxiety and depression since my teens and I remember this feeling well where I would just sob in bed as a teen because I didn't know how to cope with this depressed feeling:weep: I truly wouldn't wish it on anyone and I haven't had it for a long time and I'm just posting to feel like I'm less alone and like someone else understands? I really don't know if it is to do with me stopping mirtazapine as I have been very careful to come off it gradually with my doctor's approval, I just hate the feeling so much it makes you feel completely helpless ugh! Felt like I needed to vent this all out and thanks to anyone who reads:)