While it is possible to skip or delay a period while taking birth control pills, it is more easily achievable on products that are mono-phasic, or pills that only contain one level of hormone throughout the entire pack. As you mentioned, Ortho Tri-Cyclen Lo contains varying levels of hormones in each week. Each week for the first 3 weeks, the dose of the progesterone ingredient increases. Still, a delay is possible but you are very likely to experience some sort of side effect such as breakthrough bleeding or spotting.
Current birth control pills are designed to copy the natural menstrual cycle in women. They are used for both contraceptive purposes as well as for helping women maintain a normal menstrual cycle. There are many different kinds of oral hormonal contraceptives available, but most options contain 3 weeks of active hormonal pills and one of inactive, or placebo pills. Menses occurs during the week you take the inactive pills with no hormones in them. As soon as you stop taking pills with active hormones in them, that is when you will get your period. For those wishing to extend the time until menses occurs, you would need to keep taking active hormonal pills. Again, stopping active hormonal pills WILL bring on the onset of menses. In fact, delaying menses by one month or more is a common way of dosing and is known as continuous dosing, or continuous cycling. While many patients on continuous cycles simply skip the inactive week in their pills and move on to the next pack, newer products on the market such as Seasonale provide 3 months of active pills followed then by 1 week of inactive pills.
For those wishing to extend the time until menses occurs, you need to keep taking active hormonal pills. Skipping a week of pills all together will almost assuredly bring upon menses or some form of breakthrough bleeding or spotting.
As I mentioned in the opening, it is a little tougher to skip a period on products that contain varying amount of hormones. Being on your birth control for 4 years, you body is just so used to those fluctuations in hormone levels. If you were to extend a week of your cycle by taking another row of active pills, I can almost guarantee you would experience some breakthrough bleeding or spotting. In fact, breakthrough bleeding is the most common side effect of continuous dosing, especially during the first few months of the new therapy and especially if you have been having a normal menstrual cycle for a long period of time. Breakthrough bleeding typically decreases over time, however, as your body adjusts. This won't help much in your case since you are only looking to extend a week.
It is often hard for some patients to change from having monthly periods to having periods every 3 months or longer. Below is a graph showing the percentage of patients who had breakthrough bleeding on a continuous dosing product known as Seasonique. During the first two cycles (6 months), nearly 50% of patients experienced some sort of breakthrough bleeding or spotting, and this is after months! It simply takes time for the body to adjust to continuous dosing. You can see that trying to extend your cycle by one week all of a sudden will most likely result in some sort of bleeding unfortunately.