Yes, and virtually always related to trigger foods. (Some food I can always eat, some I can never, and some I can only eat for a little bit or things will flare up. Triggers will vary from several hours to several days or even weeks before causing problems.)
How it works with me is like this: in summer I am relatively healthy, once I have recovered from the winter. (I'm far North and have bad SAD, this doesn't help.) In winter my gut gets more grumbly, and stress or trigger foods will upset it more easily. Soemtimes, even in summer, I will get an enormous flare up just out of the blue - I am now inclined to think that is because I have fallen off the diet tightrope, and it takes a while to hit ground. I pretty much know what my week ahead is going to be like, simply by regulating my diet and physical exercise/stress levels.
I think of it as having a low-level infection all the time, but the sensitivity threshold at which I start showing symptoms varies. Sometime the bug gets really stroppy - for example after I have been eating chocolate or cheese, or had too much caffeine or sugar for a while, suddenly I get diarrhoea and bloody stool again, fevers etc. (Recently I was warned by a nutritional therapist that my salt intake has a big effect on my gut, and I should cut way back.) Accompanying this I have bouts of sudden acute fatigue to go with my usual chronic fatigue, and depression, problems with memory and concentration, and often skin and joint problems - more recently, also lower back pain.
One thing that I learned last week was that fatty or oily foods in the lower gut, if you are not producing enough digestive enzymes, will cause severe pain and repeated bouts of painful diarrhoea with fever and nausea until the colon is empty. Real "I wish I hadn't been born" territory. After that - and this "morning surprise" is something I've often had and never known why - I'm right as rain for the rest of the day,albeit feeling a bit less full of beans. But the more often I have that sort of episode, the more the episodes tend to creep closer together timewise, and the more fatigued and generally susceptible to displaying worse symptoms I am. (After a bad winter, I am only really back to "full" health in late summer.)
I see exactly where you are coming from, thinking of parasites. I too tend to have an eye
open for spirochaetes and nasty little protozoans like Borrelia Burgdorferii in particular - you might want to check out the Lyme's Disease forum here on HW. I would be extremely cautious in accepting the current received wisdom about
tests and diagnosis in mainstream medicine on this subject however - as you will see if you do any research, the diagnostic guidelines which are now set in stone were designed for epidemiological use which is another purpose entirely, and much data has been excluded from current models of the disease. (Never a sign of good science or medicine.) I don't know much about
parasites in detail, but the cyclical nature of your problem certainly makes me think that you may be on the right track, if the timing is actually regular and not just on/off in frequent succession. The timing and duration is certainly key to that diagnosis. Crohn's certainly is notorious for its acute variability, but not for being regular.
Sorry, unintended pun there (for once) !
Itchy bum, yes, very common with CD. Skin lumps and bumps - again, quite common as an extraintestinal symptom. I have tiny yellowheads and thumbnail sized purple blotches that look like bruises but never entirely fade, they come and go according to how well I am. In an extended flare, my spots become swollen and red; sometimes other invisible sore spots appear under my skin but never make to the surface, merely causing pain and swelling. As you say, rather like an insect bite, but when I know I can't have been bitten.
It is worth noting that IBS/IBD in some medical circles is very much an umbrella term for "unexplained gut illness we can't identify" - but sometimes it is taken to specifically exclude CD, UC, etc. The distinctions are pretty blurred and tend only to become clearer over a period of years.
Advice ? Yes, think about
parasites, but try some good high dose probiotics meantime - you can get a lot of info on brands by searching posts here - and if that works, you may have cut the Gordion knot.