I think I responded to your previous message but in case I didn't, here goes...
In August last year, I had significant belly bloat which ranged from looking like I was 5 months to full term pregnant, depending on the day.
I had numerous GP tests, abdominal scans, internal gynae scan (I paid privately because I was so worried) and blood tests. My CA-125 was elevated but the scans ruled out anything overly nasty. I have a history of gynae intervention so it was assumed my endemetriosis was back. However, it wasn't presenting as normal so I was sceptical.
I kept a food diary and eventually the GP agreed to run a blood test for coeliac disease which came back positive. I've had to shift my entire diet (low Fodmap as well as cutting out all wheat, gluten and dairy) and it's made a huge difference.
However, its not perfect as the bloat returns during my cycle. I'm currently my usual weight but look at least two dress sizes bigger around belly and hips. I'm going through forced menopause to see if the reduction of hormone makes a difference and, if it does, I'll be having surgery.
If you haven't alreadu, cut out wheat for two weeks and see if it helps. Check labels as it's bloody well everywhere.
If it's still there, ask go for referral for abdominal scan. This will take time, especially in the current climate, so if you're in the position to pay, id recommend for peace of mind. I think my scan was £110. It was genuinely worth every penny.
I know you're scared but it is a process of elimination so you need to start with least invasive options that you can self manage (diet) while regularly checking in with GP and getting bloods etc done