Help – Separation Anxiety

I have a brussels griffon who is 1 year and 7 months. We noticed signs of separation anxiety since 6 months and we’ve worked with a trainer who trained under Julie Naismith. He’s on max dosage for Reconcile for his weight, which he’s been on for under a year now in conjunction with gabapentin given 1.5 hours before his training sessions. We were going very slow and we were so confident that he could handle any time less than 2 hours. All of sudden, he’s sitting at the gate at 40 minutes and 2 minutes one time and not able to settle at all and he’s whining when he hasn’t done this since we started training.

Nothing has changed and we’ve been training for a year. All of this has taken a mental load on me with no support system and I’ve spent so much money on him with training (he also is reactive). I’m at a loss. What do I do? What is happening? We’re looking to switch medications but that’s a whole other process of tampering him off and I’m just so tired of trying so hard and being stuck at home for so long.