Well, taking 100mg of clomid on days 3-7 of your cycle, you have a pretty good chance of conceiving even with only one tube as long as other factors are not the problem (tube blockage, low sperm count/mobility). Clomid works by blocking hormone receptors so your body will produce more of the hormones that 'grow' your eggs. Usually that means your body will produce more than one egg to release during ovulation and will also release an egg/s from both ovaries, which is very helpful if you have only one tube. This will increase your chances for an egg to release on your good side. As for twins, it's a lower chance with you having only one tube, but still possible if two eggs (or more) are released on the good side and are fertilized. Clomid can be prescribed to start on different days of the cycle. Usually, the earlier it's prescribed the 'more' eggs produced. The later taken, it makes less eggs but of a 'better' quality or more mature. So taking it day 3-7 should make more eggs for you. Good luck!