My gums have been bleeding for years when I brush but now they also feel itchy and inflamed at times. What could be wrong?

Infection. Bleeding gums are infected gums. Swelling and tactile sensations indicate the infection is worsening. Your Oral Hygiene regimen is obviously not working. Bite the bullet, see your Dentist. Referral to a gum/bone specialist, a Periodontist, is in order. Go now before the disease does irreparable damage.
Inflammation. At a minimum you have gingivitis, hopefully not periodontitis. You need to see a dentist immediately to be evaluated and treated. Failure to do so can result in the loss of your teeth.
Bleeding gums. Bleeding gums are a sign of infection. It is not normal or healthy. You should see a dentist to evaluate the health of your gums and teeth. Treatment of bleeding gums include teeth cleaning or scaling and root planing, antimicrobials. You need to brush and floss your teeth to remove the bacteria around your teeth and gums that are causing the gum disease.
Periodontal Disease? This is something you should bring to the attention of you dentist or hygienist at your next visit. You could have gum disease, and this--like any other disease--is best treated early.
Need an exam. You need to see a dentist to really answer this but usually, bleeding gums are caused by inflammation in response to poor plaque control exacerbated by a high sugar diet. Brushing is important but so is inter-dental cleaning (flossing). If your hygiene and diet are good, there could be other issues but start with those 2. Don't let bleeding dissuade you from thorough home care as it is the answer.