Oh wow didn't expect two small cups (or absence of) would wreck you like that. Tea maybe not the best substitute then...
I think I'm very sensitive to caffeine. Some people have more tolerance for others less.
For example, before this experiment, I tried black tea. I had it around 6 pm on a Sunday. I know rather late, but I didn't think it would mess me up that bad. I could not sleep all night. I know black tea has caffeine, but I didn't' know it would affect me that bad.
I feel you. I remember back when I started to drink coffee (already was in my early thirties) I was restless and anxious for basically the whole day after drinking a single cup, basically what Naff wrote. Not even sure why I kept drinking coffee, because the feeling was really not so nice. Probably the taste and the shared social ritual (this was when I was writing my graduation work). Took me months to build up tolerance.
Even now, when I drink more than two coffees a day I will get extremly restless and can't fall sleep.
What's curious, I don't really feel like I get a boost in the morning from coffee or that I feel less awake if I miss my coffee. I kinda feel this is more some form of self-hypnosis. Like there is some effect from coffee that activates your cardiovascular-system, but I don't feel like my mind really gets going from coffee.
But what's great about coffee is that it really helped with my migraine. I definetly have less cases of migraine since dring coffee. Only problem: if I don't drink a coffee in the morning the chance for a headache actually seems to have increased.
Also regarding black tea I'm not sure if it's better than coffee regarding messing you up. At least a cup of black tea is comparable to a cup of coffee for me (although the actual coffein intake should be definetely higher from coffee to tea). Just read up on wiki that coffein from tea is released in intestine compared to the gut for coffeine from coffee. Because of that, it takes longer for the coffeine to take effect and it lasts longer. This might be a reason why tea fucks more with your sleep if you drink a blck tea in the afternoon.