As others are saying, you may need the dose increased, or it could just be taking that bit longer to take effect this time. Thing is as I'm sure you know, the ADs only deal with the symptoms, and not the underlying cause. High level anxiety is hell - anxiety really means fear - fear of the present and fear of the future. ADs are meant to cope with anxiety too of course. Another trick thid bloody illness plays on us is that an AD that worked the first time, might not do so in another episode. Maybe you will need to try another one, but you need to see your GP asap I think.
Re your partner talking of wanting his child with him all the time - this may well be a threat so that you won't leave him, as I gather he doesn't want the r/ship to end, but it is an empty threat. When parents split up and can't agree about who the child lives with, then the matter goes to the Family Court. One or other of the parent is awarded a Residence Order (meaning that that is the person with whom the child lives) whilst the other parent is almost always awarded contact, and if the parents can't agree on this, then the court defines contact, as in stating how many days of the week the non-resident parent has with the child and the hours etc. If the court accepts that there is a concern about the welfare of the child during contact, then contact will take place at a Contact Centre and wil be supervised.
The main thing that is taken into consideration is the best interests of the child. I was a social worker and middle manager in a LA social services dept and did some work in the Family Courts. Am now retired. Parents who can't agree are offered mediation, especially if they are claiming legal aid. I really do hope that you can agree that the child lives with you and the father has contact, as once you get into the Family Courts the whole thing can drag on for months on end, even years in some cases. The other thing is that I don't think legal aid is going to be available for private law cases in the Family Court, but not sure whether this has yet been withdrawn.
Judges get very sick of warring parents and the children are caught in the middle, especially when it is obvious that one of the parents is just trying to spite the other. The parent who has the child's best interests at heart and is not slagging off the other parent will best impress a judge. Your mental health cannot be "used" against you. Depression and anxiety (horrid as they are) are not the type of mental illnesses that would raise concern about the welfare of a child, as in pyschotic illnesses, which is a thinking disorder.
Hope I haven't bombarded you with too much info. Have only just noticed you were seeing a solicitor today, but some of them aren't much good I'm afraid, so if there is anything you aren't clear about I would be happy to help further.