Hi. I also have left-sided colitis. My advice is rectal meds, rectal meds and more rectal meds (Quincy will be so proud!). But also oral 5ASA (lialda, asacol).
First of all, don't just give up on lialda or asacol because you think you are allergic. The Dr should be able to test to see if you are actually allergic or showing signs of bad side-effects. If that's all ok, my advice is to up your lialda to 3 or 4 grams and day and blast your colon with nightly 5ASA enemas (Rowasa) until you are out of this flare (checking with your Dr firstly, of course). At least a month's worth of enemas with some tapering after that.
Then for maintenance, find a daily dose of Lialda that works for you and throw in a few (2-3) enemas a week. That's your maintenance routine.
There is a lot of evidence from studies that left-sided colitis benefits greatly from 5ASA enemas both to control flares AND for maintenance. Here are some links to studies I posted in a thread about maintenance rectal meds a few months ago.
You also have the option of steroids via enema (liquid or foam) if the 5ASAs don't work for you. But personally, I'd give the 5ASA oral and rectal combination a serious try before going to steroids. You may need to be patient with them but a few of us here have had great success with the 5ASA. Since I've put 2 5ASA enemas a week into my maintenance routine, I've been flare free - going on 15 months now.
Best of luck!
Effect of weekend 5-aminosalicylic acid (mesalazine) enemas as maintenance therapy for ulcerative colitis: results from a randomized controlled study.
Trouble maintaining remission in ulcerative colitis? give 'EM an enema!?
Long-term intermittent treatment with low-does 5-aminosalicylic enemas is efficacious for remission maintenance in ulcerative colitis
Medical Management of Ulcerative Colitis
here's the html version as I couldn't get the above link to load
Left Sided UC
Maintenance Meds: Salofalk tablets (Asacol) 2 tablets 4 times daily (4gm total) plus 2 Salofalk foam enemas per week.
Flare Meds: Salofalk enemas and/or Colifoam
Oat bran 60grams daily, Metamuscil and multivitamins