I keep getting bad pains in the top of my leg, front back and the inner side, the back is worse when I sit down, also when I sit the bottom of my left leg goes numb, I have started to get aches in my neck and arms,

Have you seen your doctor? The human body is a wondrously complex organism. The problem is that several different and diverse things can cause the same symptoms and it is nearly impossible to diagnose with the amount of information that can be given across the internet.

Find a GOOD chiropractor, one by reference from asking everyone you know.
(I had a fantastic one and then tried another after I moved, and that one was not good at all.)

Your leg pain sounds like sciatica (sciatic nerve) with possibly other nerves being irritated too, such as sacral.
Your neck and arms could be aching from the way you favor one side when your leg hurts... or it could be anything. You could have some spinal curvature problem. You could have something rare.
BUT big BUT
All your pain could be related to daily activity, such as how you sit at a desk! You could cure it all by changing something easy. Tell us what you do all day.

Skip the chiropractor and find a neurologist. Get your nerves all checked out first. And circulation and go from there. Trust me I have multiple sclerosis it isn't easy

I tried medical doctors for over 30 years, including a neurologist, and got nowhere.
In my case, it took a good chiropractor to listen carefully and diagnose correctly based on what I said! I have scarring on my left sacro-iliac, that causes pain of the sacral nerves in the abdomen (they wrap around to the front).

Of course a condition such as MS requires an MD. feedursoul, how long did it take you to get diagnosed, and what were your symptoms, if you are willing to say?

I tried medical doctors for over 30 years, including a neurologist, and got nowhere.
In my case, it took a good chiropractor to listen carefully and diagnose correctly based on what I said! I have scarring on my left sacro-iliac, that causes pain of the sacral nerves in the abdomen (they wrap around to the front).

Of course a condition such as MS requires an MD. feedursoul, how long did it take you to get diagnosed, and what were your symptoms, if you are willing to say?

Took them 4 years to finally say "OK" you do have MS. While the whole time they were saying you very well could have MS. Crazy docs. Symptoms were insane. Muscle spasms, circulation issues, feeling like things are crawling on you (because my nerve ending are fried or dead), eye sight changes, memory loss, lots of pain, body cramps, sleep issues, etc etc

Does that help answer your question?

YES thanks.
I have heard that it almost always takes a long time to finally decide on MS as a diagnosis. I guess there's still no quick tests or ways to rule out many other conditions. I hope you have ways to alleviate those horrible symptoms now.
I think it's good that we both gave our own slant to the original question.
It could be something else too, serious or not.
Someone was here not long ago who has similar symptoms and it turns out he spends a lot of time sitting up in bed using his computer! I said that is obviously the first thing to correct before running to specialists. Do you agree?