Welcome Denise and Pumpkin! A diagnosis of diabetes can be overwhelming especially in the early days. We strongly advocate home testing here because BG readings taken at the vet are usually elevated due to stress and that often leads to the vet prescribing more insulin than what is needed. Home testing allows you to ensure that insulin is only given when it's safe to do so and to check how the insulin is working while kitty is relaxed in their normal environment.
A dose of 2 units daily is not unusual if given as 1u twice daily but I notice you mentioned the original dose was 1.2u once daily and that is unusual and not very effective in the majority of cats. Lantus is usually given every 12 hours so if you are giving the 2 units once daily that could be part of the reason why you are seeing higher numbers now. 2 units at once daily dosing would also be a larger dose increase than we would recommend. Both once daily dosing and increasing the dose too much can lead to bouncing.
Bouncing occurs when kitty's BG falls quickly, falls to a level the cat is no longer accustomed to or if the BG did in fact go too low at some point. There is a natural defense system that pumps out other hormones to bring BG numbers back up often to even higher levels and in a diabetic their defense system gets out of kilter and revs into action often earlier than necessary. As kitty gets reacquainted with normal BG levels the defense system will recalibrate and the bouncing phenomenon lessens with time.
The other potential impact on Pumpkin's BG may be the diet the vet prescribed. You didn't mention if the prescription food is wet or dry but many of the so called diabetic prescription diets have higher carbs than many store brands of wet food and they certainly are considerably more expensive and unnecessary. Lots of dietary info available
HERE.
It's early days yet and this is a marathon...not a sprint. Each cat is a unique individual and the amount of insulin a cat requires is an individual matter.
If you are interested in learning to home test Pumpkin, we can help. Home testing not only gives you more accurate BG readings but it also decreases costs associated with repeated vet visits not to mention lessening the stress of those visits on both you and Pumpkin. A human glucometer can be used and many folks in the US use either the Relion Confirm or Micro from Walmart. We have a spreadsheet available here to keep a log of the home readings which can then be shared with your vet and viewed by the community here so if you need help at any time, we can view the data you have collected and offer whatever help you need.
Keep asking questions and let us know how we can best help you!