There are certain creams on the market which supposedly help with stretch marks. Tretinoin cream (commonly known by the trade name Retin-A) has been shown to be effective in scientific studies.
I would advise not going sunbathing until they fade. Tanning will make them stand out more.

This is another secret i learned from my grandpa (funny enough). Most people don’t think that guys get stretch marks, but ask any weightlifter and they will tell you guys get them all the time. You see during the depression he was forced to manually move his rock fence 100 yards dead west of his property line because the propery lines were drawn incorrectly and the desperate state of the city said they needed his fields for irrigation purposes. Anyways, he was forced to carry over 500 tons of rock with his bare hands over a 1 year period to save the farm. (he had his 4 brothers helping almost 10 hours a day 6 days a week) He developed huge stretch marks on his chest from the excessive lifting and increased muscle growth (guys get them when they grow muscle too fast). He told me once that the easy way to get rid of them is to rub the marks down with olive oil for 20 minutes a day. AFter the oil is applied then you want to apply salt over the marks, This is suppose to dry the skin causing the skin to fuse together where it was stretched. He said to only leave the salt application on for about 5 minutes each day. He had those “ugly stretch markes” (he use to call them) for 10 years and then in 1954 after a week of doing this application they disappeared forever. I hope it works for you.