There are multiple potential causes of your pain, including gynecologic, gastrointestinal, and musculoskeletal etiologies. You should see your doctor who can take a more detailed history, perform a physical exam, and/or order imaging tests. One thing to consider is pelvic congestion syndrome, characterized by chronic pelvic pain exacerbated by standing or sitting for long periods of time. This can be further evaluated with CT abdomen/pelvis or MRI pelvis with contrast.
Sounds like you might have a possible UTI.
Hi and welcome to the forum. So, how long has this been going on? Nothing happens before it except sitting for a while and then standing up? Sharp pains make me think you need to see a doctor asap. Is that a possibility for you? There is something called interstitial cystitis (IC). It has pain like this but usually some other symptoms. Any trouble with urination?
Your doctor can check urinalysis and/or urine culture to rule out urinary tract infection.