One great source could be fanfiction.net. There are often many stories in the 'Bitten' fandom that might feature Elena and Clay in a pregnant storyline. You can search using the tags related to 'Bitten', 'Elena', 'Clay', and 'pregnancy' to narrow down the results.
You could try reaching out to 'Bitten' fans directly. Join a 'Bitten' fan group on Facebook perhaps. Explain what you're looking for - a Elena and Clay pregnant fanfiction with a happy ending. Fans who are more familiar with the available stories might be able to recommend a great one to you. They may have read many more stories than you could search through on your own and can give you some really good suggestions based on their own reading experiences.
Some plotlines in Clay and Elena pregnant fanfiction involve their friends' reactions. Their friends could be super excited and throw them a baby shower, or there could be some jealousy or envy among their friends who are not in the same life stage. Also, the pregnancy could be unexpected, and they have to quickly adjust their lives. Maybe Clay was planning to focus on his career and now has to shift his priorities. Elena might be dealing with morning sickness and Clay has to learn how to take care of her while also handling his own responsibilities.
Clay might become more responsible. With a baby on the way, he could start thinking more about the future and taking on more tasks to support Elena and the unborn child. For example, he might take on extra jobs or start saving money more seriously. Elena could become more nurturing. Her focus would shift from just herself and Clay to also include the baby. She might start learning about childcare and become more patient as she anticipates motherhood.
One common theme is the struggle for survival. Since Elena has been bitten, she has to fight to stay alive, both physically from the effects of the bite and also against any potential threats that come with it. Another theme could be the change in relationships. For example, her friends and family might react differently to her now that she's been bitten.
Another option is to look on Wattpad. Although the quality can vary greatly, there are a large number of fanfiction works on there. Try using the search terms 'bitten Elena hurt' and skim through the results. Some stories might be really well - written and give you a great take on Elena's situation after being bitten, including her emotional and physical hurt.
One interesting fanfiction could be where Elena's bite leads to a new power awakening. For example, instead of succumbing to the venom, she discovers she can control the vampires that bit her. This changes the power dynamic in Mystic Falls.
Another aspect could be how they plan for the future. They might decide to move away from Mystic Falls to start a new life. This would involve leaving behind their vampire - filled world and trying to build a normal life for their baby, which is full of both difficulties and hopes.
One great 'Elena pregnant' fanfiction is 'Elena's New Chapter'. It beautifully explores how Elena's pregnancy changes her relationships with other characters. It has a really interesting plot where she discovers new sides of herself during this special time.
Another theme is self - discovery. Elena usually discovers new things about herself during pregnancy. She might find new strengths or weaknesses. In some fanfictions, she learns that she can be more independent or that she needs more support than she thought.