Confusion & Aphasia after infection

I care for my partner who has PPMS and is advancing rapidly since his diagnosis only a few years ago. He is now in a wheelchair with limited use of his arms and hands.
Since his diagnosis he has had a serious blood clot in his thigh/abdomen and sepsis. After both he returned to his normal character and worked through his worsened symptoms to regain as much of his previous ability as possible.
About 10 days ago he was showing signs of potential sepsis and we cycled through out of hours care and into A&E by ambulance. He was treated there but there was no major infection found so they sent him home with antibiotics. Whilst his temperature came down on the antibiotics he hasn’t been himself since and has none of the fight to recover - he sleeps a lot, keeps his eyes closed for the most part, has changed character from his normal self and is suffering from aphasia and/or confusion most of the time to the extent it can be impossible to communicate with him because he is saying things that make no sense at all. If I can get him to engage in a conversation with me then he says he is fine.
What do I do? I feel like I need to call in more medical advice in case something else is going on here - but am I over thinking? My gut tells me something isn’t right…