chasing but he is at risk from his daddy, as are you. This is common practice with DV. The police would have put in some kind of report as there was a baby involved. The fact you are seeing your GP about PND shows you are doing your best to safeguard you and your son. SW will want to see if there is any additional support needed. I urge you to discuss alternative accommodation, and also request supervised access. They may be able to get a nursery place for J to give you a wee break, and can help in other ways, financial advice, referral to other agencies. I totally understand you being worried, but honesty is the best policy. Do not protect your ex, and see this as an opportunity.
Any agency referring to SW should have the decency to tell the parent, so i doubt it is the HV or GP. Police do not need to as it can aggravate the situation. There is an outside chance that your ex or in-laws have reported a concern, but even if that is the case, you still do not need to worry. Do not worry about the house being spotless, just try to remain calm. It may help to write things down before they visit - what has happened, what you fear, what you want etc.